PG AND RESEARCH DEPARTMENT OF MICROBIOLOGY,SRI PARAMAKALYANI COLLEGE,ALWARKURICHI

2. CONTENT
• Introduction
• Identification of heterocyst
• Definition
• Heterocyst types
• Position of heterocyst
• Structure of heterocyst
• Development of heterocyst
• Factors affecting development of heterocyst
• Function of heterocyst

3. INTRODUCTION
• Thurrers 1844 was the first to report these cells in blue green algae especially in order
nostocales and stigonematales,except osillatoriaceaefamily.
• Heterocyst are found in many species of filamentous blue green algae.
• They are cells of slightly larger size and with a more thickened wall than
the vegetative cells .

4. IDENTIFICATION
• They are usually larger than vegetative cells, develop thick tegumentary
layers and intracellular hyaline button at the point of attachment to
the vegetative cells, displaying a pale reduced autofluorescence.
• Such as heterocyst are easy to recognize under the microscope.

5. DEFINITION
• Heterocyst are specialized Nitrogen fixing cell
formed filamentous cyanobacteria during periods
of Nitrogen starvation.
• A heterocyst is a differentiated cyanobacterial cells
that carries out nitrogen fixation.
• Nitrogen fixation is a conversion of atmospheric
Nitrogen (N2) to Ammonia (NH3) In order to
build organic molecules .

6. • It contain Nitrogen fixing enzyme Nitrogenase.
• Example of cooperation – heterocysts and photosynthetic cells in same filament
exchange metabolic products.
• Which is inactivated by oxygen,so heterocyst create an anaerobic environment
by , 1. making 3 extra cell walls ,
2 .degrading photosystem -2,
3.producing oxygen scavenging species.

7. HETEROCYST TYPES
• They have evolved multiple specialized cell types ,including Nitrogen
fixing heterocyst,spore –like akinetes,and the cell of motile
hormogonia filaments of these,the development of heterocyst in the
filamentous cyanobacterium anabaena (also Nastoc) species

8. POSITION OF HETEROCYST
• Heterocyst usually occur singly,In same species in pair and rarely in chain.
• When they occur singly they are terminal or intercalary in position.
• Lateral heterocysts are found in Nostochopsis

9. STRUCTURE OF HETEROCYST
• Heterocysts are,pale yellow and barrel shaped Structure.
• These are covered by envelope and cell wall.
• Envelope of heterocyst is nade up of three layer.
• Outer loosely fibrous layer,middle homogenous layer and inner lamillated layer.
• Middle and inner layer are of uniform thickness except at the poles where they
are more thicker .
• All the layer of envelop surrounds the heterocyst except at the junction of the
heterocyst with vegetative cell.

10. • The cell wall of the heterocyst is made up of four layer as in vegetative cell.
• Cytoplasm include an abundance of carotenoids and a little amount of chlorophyll a but
phycobilins are absent.
• Photosynthesis absent.
• DNA is present in the cytoplasm.
• All other granules and gas vacuoles are also absent.
• At the junction between heterocyst and vegetative cells there is deep constriction.

11. • Intercalary heterocyst has two pores where as terminal heterocyst has a single pore.
• Plasmadesmeta are present on plasma membraneto connect vegetative cell and
heterocyst.

12. DEVELOPMENT OF HETEROCYST
• Any vegetative cell divide and forms two daughter cells.
• One or both the cells may behave as proheterocyst
• Proheterocyst enlarger in size secretes a multilayered envelop out site the cell wall.
• The pores appear at one or both the ends.
• In a mature heterocyst pores become blagged with refractive material.
• There are called the polar granules.
• Now Cytoplasm connection with adjacent cell is broken .

13. FACTORS AFFECTING DEVELOPMENT OF
HETEROCYST
• Blue green algae light inhipits whereas white and red light supports.
• Concentration of Phosephatesalts stimulate heterocyst formation.
• Absence of Megnesium and iron inhibit heterocyst formation.
• Presence of compained Nitrogen is also have inhibitory effects.
• C:N radio also play an important role in inducing heterocyst formation.

14. FUNCTION OF HETEROCYST
• Storehouse of reserve food materials.
• Sites of Nitrogen fixation.
• Locus for filament breakage.
• Play role in sporulation.
• Vestigial reproductive Structure.
• Produce substance which stumulates cell divition and growth.