This presentation briefly describes the methods by which stem reserve mobilization occurs with some case studies proving the occurrence of stem reserve mobilization. Also trying to explain the mechanism

1. University Of Agricultural Sciences, Dharwad
Department Of Crop Physiology
Master’s Seminar I
Stem reserve mobilization and sink activity under
drought and heat stress
Brahmesh Reddy B R
PGS20AGR8436

2. One who solves the problem of water is worth TWO
NOBLE PRIZES
one for SCIENCE and one for PEACE
- John F Kennedy
35th US president

3. Note that the most the work on SRM has been done
in wheat cultivars, so case studies have been picked
in the Wheat
The stem reserve mobilization in sorghum, bajra, and
other millets including chickpea and many other
cereals and pulses occurs significantly similar to that
of wheat

4. In brief of what we will be discussing
Photosynthesis in leaves
transport to sinks
stem as a sink
initiation of grain filling
unexpected stress
unable to fulfill grain sink requirements
assimilates accumulated in the stem
compensate of this shortage and is moved
to grains

5. Demonstration of stem reserve
mobilization
A Blum

6. Chemical desiccation treatment
of wheat breeding materials
a spray treatment to induce desiccation
(Also can be used to screen the genotypes for drought tolerance)

7. Principle
This method does not simulate drought stress. It simulates a
condition where grain filling proceeds with no transient
photosynthesis, relying mainly on use of stem reserves. The test is
performed by comparing the reduction in kernel weight from
controls to the treated plots.
Time of treatment
13 to 15 days after heading to coincide with onset of the
exponential phase of grain filling.
The desiccants like magnesium chlorate or potassium iodide
0.4% a.i. can be used

8. How to find out reserve mobilization
% reduction in kernel weight by chemical desiccation is obtained by
comparing mean kernel weight under desiccation with mean kernel
weight in the control
0.4% KI Control 0.4% Mg(ClO4)2 Control

9. Situations under effect
A Blum

10. Grain filling
often occurs when temperatures
are increasing and
moisture supply is decreasing.
The common end-result of these stresses is kernel
shriveling, reduced test weight and loss
in yield

11. Situations under effect
Current assimilation, as a source of carbon for grain filling,
depends on the viable light intercepting green surfaces of
the plant after anthesis.
Natural senescence
Demand for growing kernels
Maintenance and respiration
This source normally diminishes due to natural senescence and the effect of
various stresses. At the same time the demand of the growing kernel increases,
in addition to the demand due to maintenance and respiration of the live plant
biomass

12. Situations under effect
Canopy respiration ≈ dry matter accumulation (stems)
(In terms of sink strength)
And fulfilled by the canopy photosynthesis
But at the time of grain filling
Canopy respiration + dry matter accumulation
>>>
canopy photosynthesis
canopy respiration and grain dry matter accumulation sites are approximately equal
sinks for photosynthates and, together, are greater than canopy photosynthesis late in
grain filling. Thus stem reserves are essential for completed grain filling.

13. How can we sense the movement
of sugars
Relations with stem dry matter
J Willenbrink and I F Wardlaw

14. Let us understand some important parts of wheat
plant that we will be discussing further
Peduncle

15. Non structural carbohydrates
(largely fructans) accumulate in
the stems up to 15 to 20 days
after anthesis
a comparison made in kernel development stage between
the rate of kernel filling and mobilization of stem reserves
over the same period, these reserves can account for more
than 50% of kernel requirements at this stage

16. Peduncle Penultimate Control
Mild Stress
Severe Stress
Control
Mild Stress
Severe Stress
Reduction of stem dry weight at various rates in different stress levels

17. So what does this tell us ?
Along the reduction in the water levels , the levels
water soluble carbohydrates also drops
Changes in stem dry weight provide an indication
of the mobilization of non-structural (reserve)
carbohydrate in response to water stress

18. In Peduncle
Controls
Dry weight
Sucrose
Tot. WSC
Fructose
Reduction of stem dry weight and water soluble carbohydrates

19. In penultimate internode
Controls
Dry weight
Sucrose
Tot. WSC
Fructose
Reduction of stem dry weight and water soluble carbohydrates
Intermittent increase in the dry weight between 24th and 26th DAA is
concurrent with the rise in the fructose levels
Drastic increase
of fructose is
from fructan
breakdown
A large part of the
drop in dry
weight of the two
internodes in the
period 26–32 daa
(c. 70%) could be
accounted for by
the fall in total
WSC over the
same period.
Glucose

20. In penultimate internode in severe stress
Sucrose
Tot. WSC
Fructose
Reduction of stem dry weight and water soluble carbohydrates
Glucose
As with mild stress, the changes during severe stress were greater in the
penultimate internode than in the peduncle, but the patterns were
similar.
From 23 to 25 daa there
was a fall in dry weight of
both internodes, of which a
considerable part (c. 65%)
could be accounted for by
the mobilization of WSCs.
Dry weight

21. Can we arrive at a thought that SRM only
participates in grain filling?
NOOO….
The observation that there is an initial rise in low
molecular weight sugars in the stem of wheat
entering water stress suggests a degree of osmotic
adaptation and therefore a possible protection
against dehydration.

22. Even the deepest studies on the stem reserve mobilization have not
able to reveal about how the water stress induced the increase in
biosynthesis of FEH and what initiated the transport of sugars into
the grains

23. Factors affecting the stem reserve
remobilization
1. Nitrogen application
2. Soil moisture levels
3. Activation and inactivation of enzymes
4. Sowing conditions
5. Maximal and minimal temperatures

24. CASE STUDY 1
Remobilization of carbon reserves is
improved by controlled soil drying during
grain filling of wheat
Jianchang Yang, Jianhua Zhang, Zuliu Huang, Qingsen Zhu,
and Long Wang
for Factors 1 & 2

25. Particulars under study
Soil conditions and N levels
All the treatments are the initial levels and these will change as the treatment time progresses
Cultivars
Yangmai-158 (Y 158) Yangmai-158 (Y 158)
Semi- winter wheat cultivar (pot) Winter wheat cultivar (field)
Yangmai-931 (Y 931)
Semi- winter wheat cultivar (pot)
-0.02 MPa (WW)
Well watered
-0.04 Mpa (MD)
Mild soil drying
-0.06 Mpa (SD)
Severe soil drying
0.5 g N (NN)
urea per plot NN-WW NN-MD NN-SD
1.2 g N (HN)
Urea per plot HN-WW HN-MD HN-SD
The above mentioned treatments are with respect to pot experiment and since in the field
experiment, not so many combinations can be used. Hence only 4 combinations which includes
WS as Water stressed along with two levels of N are used.

26. Comparing related factors (pot expt.)

27. Comparing related factors (field expt.)
A similar trend in the decrease of photosynthetic rate is
observed relative to the decrease in the soil water potential

28. Comparing related factors (pot expt.)

29. What does the this triple comparison tell us ?
Reduced water potential
Reduced availability of water to plant
Chlorophyll degradation => reduced chlorophyll content
Reduced photosynthetic activity
Reduced production of photo assimilates

30. Important observations
Photosynthetic rate and chlorophyll content was
during the grain filling stage
But
both declined very slowly under all
Well Watered and High Nitrogen treatments
than those of NN treatments combined with different levels of soil drying

31. Let us look into the effects caused by nitrogen
POT
FIELD

32. NSC in the stem and sheath was
substantially reduced 15 DAA
The reduction was faster under
the NN treatment than under
the HN treatment
Which suggests that high
nitrogen levels can improve the
mobilization on carbon reserves
POT
Approx. 15 days after anthesis
Let us look into the effects caused by nitrogen

33. NSC in the stem and sheath was
substantially reduced 17 DAA
The reduction was faster under
the NN treatment than under
the HN treatment
Which suggests that high
nitrogen levels can improve the
mobilization on carbon reserves
FIELD
Approx. 17 days after anthesis
Let us look into the effects caused by nitrogen

34. LET US TRY TO THINK OF PROBABLE MECHANISM FOR IMPROVED
REMOBILIZATION UNDER HIGH NITROGEN APPLICATION
The reduction was faster under the NN treatment than under the HN
treatment
Which suggests that high nitrogen levels can improve the mobilization
on carbon reserves
High Nitrogen
High biomass production
Large amount of reserves produced during pre anthesis period
Hence Large amounts of reserves can be remobilized
NOT FROM THE RESEARCH ARTICLE…FORMULATING HYPOTHESIS THAT’S IT
YOU COULD ALSO SUGGEST ONE…

35. WE SHALL HAVE A LOOK IN TO THE
ACTUAL NUMBERS FROM THE TABLES
As for this reason the HN treatments also left more NSC unused
than the NN treatments
The apparent percentage of remobilized reserves, their
contribution to the grain weight, transfer ratio of total NSC and
harvest index were all significantly enhanced by soil drying in both
the pot and field experiments

36. Remobilization of the assimilates to the grains was increased
by soil drying treatment
We shall observe from a general perspective rather studying particular variety
Kindly note that as we move down the table in soil drying category, there is
reduction in water potential of soil ( i.e. increased water stress)
Down
the
table
Water
stress
increases

37. Remobilization of the assimilates to the grains was
increased by soil drying treatment
We shall find evidences from the table below for the above statement
Kindly observe the letters in
remobilized C reserve column which
indicate statistical significance
What we observe is that
with increase in water stress
(WW<MD<SD)
The statistical significance in remobilized C
reserve column also increases respectively
i.e.
WW => c
MD => b
SD => a
So this means that the increase in statistical significance is indicator to us that the higher the
water stress higher is going to be the remobilization of stored carbohydrates
Stress ∝ amount of carbon reserves remobilized

38. Remobilization of the assimilates to the grains was
increased by soil drying treatment
Similar trend is also observed in case of
Kindly observe the letters in Contribution in
grain column which indicate statistical
significance
What we observe is that
with increase in water stress
(WW<MD<SD)
The statistical significance in Contribution in grain
column also increases respectively
i.e.
WW => c
MD => b
SD => a
So this means that the increase in statistical significance is indicator to us that the higher the
water stress higher is going to be the remobilization of stored carbohydrates
Stress ∝ Contribution of Carbon reserve remobilization in grain filling

39. CASE STUDY 2
Remobilization of carbon reserves is
improved by controlled soil drying during
grain filling of wheat
( an experiment using 14CO2 radioactive labelling )
Jianchang Yang, Jianhua Zhang, Zuliu Huang, Qingsen Zhu,
and Long Wang

40. Particulars under study
Wondering how radioactive 14CO2 entered the plants
Flag leaves were enclosed in a polythene chamber and sealed with
plasticine to form gas tight chamber
6 cc (=mL) of air was drawn out of the chamber and replaced with same
volume of gas containing 10 mmol L-1 at specific radioactivity of
14C at 1.48 MBq L-1
the treatment was given for a period of 30 minutes
MBq/L - Mega becquerel per Litre (measure of radioactivity)

41. So what do the observations have to tell us?
At maturity
73 – 80 % in MD-NN
88 – 92 % in SD-NN
14C fed to the flag leaves was partitioned into grains under
respective nitrogen and water stress
While it was only 60 % under WW conditions
This indicates that more radioactive C was remobilized and
deposited into grains by soil drying

42. So what do the observations have to tell us?
When compared to their respective WW treatments,
grain filling rates for all the cultivars under all the MD and SD
treatments were increased by soil drying
GRAIN FILLING UNDER WATER STRESSED CONDITIONS
>>>
GRAIN FILLING UNDER WELL WATERED CONDITIONS
Also when extra nitrogen was applied i.e. under HN conditions at
heading stage, the increase in grain filling rate by soil drying was even
more prominent

43. Conclusions from the expt.
The declines of photosynthesis and chlorophyll content in the
flag leaves were closely associated with the decline of non
structural carbohydrates
Suggesting that,
Reallocation of assimilates was initiated

44. CASE STUDY 3
Changes of enzyme activities associated with
the mobilization of carbohydrate reserves
(fructans) from the stem of wheat during
kernel filling
J Willenbrink, G D Bonnett, S Willenbrink and I F Wardlaw

45. Particulars under study
Enzymes
Fructan exohydrolase (FEH)
breaks fructan to fructose which is required during resynthesis of
sucrose before phloem loading
Invertase (INV) Sucrose Synthase (SuSy) sucrose phosphate synthase (SPS)
Cultivars
Lyallpur 73 (L)
Short – strawed wheat with moderate stem => low stem storage
Oligoculm (O)
Low tillering heavy strawed => more stem storage

46. Particulars of study
Time of study
Started soon after anthesis
Anthesis is that stage of wheat phenology that is most sensitive to
any type of stress and also the grain filling starts after anthesis
Parts of interest
Peduncle & Penultimate internode
Since these parts are the ones that develop just before the
beginning of anthesis
Rapid increase in the dry matter of the these parts is evident

47. Particulars of study
Conditions
Shaded De - grained
The leaves were shaded with the
50 percent shade cloth
All the spikelets were removed
except the 5 central spikelets
The capacity of the source to
produce the photo assimilates is
greatly reduced
The sink demand is reduced
i.e. the sink strength is reduced

48. Changes of stem sugars
F - fructose
G - glucose
S - sucrose
D - fructan

49. Changes of stem sugars (penultimate)
In the
control,
there was a
steady
decrease in
fructans (D)

50. Changes of stem sugars(penultimate)
In the
degrained
which means
sink limited
there was a
steady raise in
accumulation
or synthesis of
fructans

51. Changes of stem sugars (penultimate)
Shading i.e. the
reduced source
capacity accelerated
the loss of fructan
Reduction
244 µmol g-1 f.wt.
61 µmol g-1 f.wt.

52. Changes of stem sugars(penultimate)
Shading also
caused the loss of
sucrose
Reduction
70 µmol g-1 f.wt.
24 µmol g-1 f.wt.

53. Loss of fructans
550 µmol g-1 f.wt.
83 µmol g-1 f.wt.
Changes of stem sugars
Loss of sucrose
94 µmol g-1 f.wt.
30 µmol g-1 f.wt.
(peduncle)

54. Changes of enzyme activity
The FEH activity is
inversely proportional to
the concentration of
fructan
(fructan
catalyzes
breakdown
of fructans
and
formation
of fructose)
*before
application of
shading the
initial
concentrations
will be same
Green - increase
Red - decrease

55. Changes of enzyme activity
The FEH activity is
inversely proportional to
the concentration of
fructan
Green - increase
Red - decrease

56. Changes of enzyme activity
The FEH activity is
inversely proportional to
the concentration of
fructan
Notice the
conc. of
fructans in
in the
degrained
(reduced sink
strength)
wheat
Comparatively
the reduction
is very low
Green - increase
Red - decrease

57. Two questions
So what does this enzyme activity signify?
&
What does the fall in fructan and sucrose levels signify?

58. Changes to grain dry weight
The ear dry weights
of shaded plants
are on par with
that of the controls
The individual seed
dry weights of
shaded plants are
on par with that of
the controls

59. Changes to grain dry weight
Have you noticed?
The individual
grain dry weights of
degrained plants
are more than the
controls also.
What could be the
reason ?

60. What can we incur from increased enzyme activity
And reduced fructans and sucrose ?
The shaded plants were able to utilize the stored stem reserves
(mostly fructans and sucrose) most efficiently
Why shading…why is it considered here ?
Shading represents reduced chlorophyll activity…
Similar to or which may occur by
Degradation of chlorophyll in drought and heat stress
Inability to carry out photosynthesis due to receding moisture

61. Inferences
In the shaded (stressed) plants, where the loss of stem reserves
is clearly accelerated, there is activation / enhanced synthesis of
FEH enzyme (converts fructan to fructose) which suggests that it
is an important factor in reduced source capacities and can
buffer for the fluctuations created by environmental stresses
And
In case of completely reduced supply of current assimilates, the
stem reserve mobilization mechanism can fulfil the sink demand
to highly accepted levels

62. This is all that is related a single carbohydrate
fructan and enzyme FEH
but
this is true for all the enzymes mentioned
INV SuSy SPS

63. CASE STUDY 4
Effects of post anthesis heat stress on stem
reserve mobilization, canopy temperature
depression and floret sterility of wheat
cultivars
S Sikder and N K Paul

64. Particulars of study
Sowing
Regular sowing date
So heat stress at the growing stage
Late sowing date
This condition coincides with the terminal heat stress and also
during the growing stage
Cultivars
Gourab, Sourav, Kanchan, Shatabdi
All the above mentioned are heat tolerant
Sonara and Kalyansona
These are heat sensitive

65. Contribution of stem reserves
to grain filling
T
S
T – heat tolerant genotypes
S – heat sensitive genotypes

66. The contribution under normal condition
varied from 11.9% to 15.1% in tolerant G.
Contribution of stem reserves
to grain filling
T
S
T – heat tolerant genotypes
S – heat sensitive genotypes
`

67. The contribution under normal condition
varied from 18.7% to 21.3% in sensitive G.
Contribution of stem reserves
to grain filling
T
S
T – heat tolerant genotypes
S – heat sensitive genotypes
`

68. The contribution under late sowing
condition varied from 20.5% to 26.3% in
tolerant genotypes
Contribution of stem reserves
to grain filling
T
S
T – heat tolerant genotypes
S – heat sensitive genotypes
`

69. The contribution of stem reserves under
late sowing condition varied from 35.3% to
37.3% in sensitive G.
Contribution of stem reserves
to grain filling
T
S
T – heat tolerant genotypes
S – heat sensitive genotypes
`

70. So what were our observations from these cultivars?
irrespective of sowing time, the heat sensitive cultivars showed
higher PSR (pre-anthesis stem reserves) mobilization to the final
grain weight compared to the heat tolerant cultivars.
T
S
>
>
>
>
>
SRM in Sensitive
>>>
SRM in tolerant

71. BUT
Sowing time had marked influence on pre anthesis stem reserves
mobilization to the final grain weight
T
S
>
>
>
>
>
Both the heat tolerant and
heat sensitive cultivars
showed a common tendency
of higher mobilization of
reserves to grain under post-
anthesis heat stress condition.

72. Implications
This indicates that heat tolerant cultivars showed a less dependence on
stem reserves for developing grain.

73. So it that we can induce higher levels of stress to
get higher yields?
No…not at all !!!
Lets find out why…