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Plant structure and growth 2

This document provides an overview of the course contents for BIO 304 Plant Structure and Physiology, including details on assessment, topics covered such as plant growth and structure, and objectives to understand how plant structure relates to function and the stages of plant growth and development. Examples are given of differentiated plant cell types and primary and secondary growth in plants, with diagrams illustrating topics like the role of the vascular cambium and the anatomy of a tree trunk.

Education◦
BIO 304 Plant Structure and Physiology
Assessment • 60 % exam 40% coursework • CATs 2 = 20% • Practical work 10% • Individual task 10% 2
Bio 304 Contents • Plant structure and growth • Plant transport • Plant nutrition • Plant growth substances (hormones) • Photosynthesis
BIO 304 Part 1 Objectives:Objectives: at the end of this section the student will be able to: Relate plant structure to functions Describe the main stages of plant growth, development
Plant growth • Annuals –life cycle is complete in one year; it germinates, flowers and dies. • Biennials- life cycle takes 2 years. First year- plant grows leaves, stems, and roots (vegetative structures), then enters a period of dormancy over the colder months- next season it flowers and dies. • Perennials- grows for more than 2 years 5
Ancient trees 4700+ Bristlecone pine Baobab - 6000 yrs old? 6
A1 Overview of primary and secondary growth A = in woody stems, lateral meristems add secondary growth, increasing the girth of roots and stems B = Apical meristems add primary growth in length
A1 Overview of primary and secondary growth (cont.) C = The vascular cambium adds secondary xylem and phloem D = The cork cambium adds secondary dermal tissue
A 2A 2 Revision ofRevision of importantimportant plantplant tissuestissues:: Dermal-,Dermal-, ground- andground- and vascular tissuesvascular tissues
A2 Overview of important plant structures
A 3 Examples of differentiated plant cells Parenchyma cells A relatively unspecialized plant cell type that carries out most of the metabolism, synthesizes and stores organic products, and develops into a more differentiated cell type (see next slides).
A 3 Examples of differentiated plant cells Collenchyma cells A flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growth. They e.g. support young parts of the plant shoot
A 3 Examples of differentiated plant cells Sclerenchyma cells A rigid, supportive plant cell type usually lacking protoplasts and possessing thick secondary walls strengthened by lignin at maturity. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and is the primary constituent of wood.
A 3 Examples of differentiated plant cells Xylem The tube-shaped, nonliving portion of the vascular system in plants that carries water and minerals from the roots to the rest of the plant. The water-conducting cells of the xylem Tracheid A water-conducting and supportive element of xylem composed of long, thin cells with tapered ends and walls hardened with lignin.
A 3 Examples of differentiated plant cells Sugar-conducting cells of the phloem Phloem The portion of the vascular system in plants consisting of living cells arranged into elongated tubes that transport sugar and other organic nutrients throughout the plant.
A 3 Primary tissues in young roots
A 4 Secondary Growth 1 = Primary growth of the apical meristem is nearing completion. Vascular cambium has just formed. 2 = Primary growth continues in apical bud. In this section only secondary growth occurs. Stem thickens as vascular cambium forms secondary xylem to the inside and secondary phloem to the outside.
A 4 Secondary Growth 3 = Some initials of the vascular cambium give rise to vascular raysvascular rays Cambium cells that produce radial lines of parenchyma cells known as xylem rays and phloem rays.
A 4 Secondary Growth 4 = When cambium’s diameter increases, the secondary phloem and other tissues (including epidermis) rupture because they no longer divide and cannot keep pace. A second meristem, the cork cambium, develops from parenchyma cells in the cortex. The cork cambium produces cork cells, which replace the epidermis.
A 4 Secondary Growth 5 = In year 2 of secondary growth, vascular cambium produces more secondary xylem and phloem; cork cambium produces more cork. 6 = Stem diameter increases, the outermost tissues exterior to the cork cambium rupture and are worn off.
A 4 Secondary Growth 6 = As the stem’s diameter increases, the outermost tissues exterior to the cork cambium rupture and are shed 7 = When none of the cortex is left, the cambium develops from phloem parenchyma cells 8 = The cork cambium and the tissues it produces are called periderm 9 = bark consists of tissues exterior to the vascular cambium
A5 Growth rings in tropical trees • May not have them unless the tree is growing in areas which have definite wet and dry seasons • Dry season would act like cold winter, and slow growth. • Start of wet season would promote growth again, so rings may be visible 22
A 6 The role of the vascular cambium A = Secondary xylem and secondary phloem being added in equal amounts. NOTE: cambial initials produce much MORE Xylem. B = A cambial initial can divide to from a new initial (= undifferentiated cell) and either a secondary xylem cell (X) or secondary phloem (P) C = A cambial initial (C) can divide to form two cambial initials, increasing the circumference of the vascular cambium
A 6 The role of the vascular cambium D = Most of the thickening is from secondary xylem
A 7 The anatomy of a tree trunk A = Secon-A = Secon- dary xylemdary xylem B = BarkB = Bark
26
Morphogenesis in plants: control of organ development • Development of flowers from meristem has been studied in Arabidopsis thaliana (thale cress) • Easy because: small size, many seeds, rapid life cycle, small genome, easy to cause mutations. • Meristem cells are undifferentiated • 3 organ identity genes code for proteins that cause cells to differentiate into whorls of flower. 27
Arabidopsis thaliana 28
A 8 29 If only A only sepals If A and B sepals and petals If A and C sepals and carpels If only C only carpels
The ABC hypothesis 30
31 Genes (a) The four organs of a flower —carpel (yellow), stamens (green), petals (purple), and sepals (pink)—grow in whorls that develop from meristems. Mutation in one of three organ identity genes occurs one type of organ replaces another. Mutations helped scientists know the pattern of gene expression that p roduces normal flowers
Application: Two uses in horticulture/agriculture A9 32 C genes control development of carpels Carpels develop into grains we eat More active C genes more carpels  more food Transgenic orange trees containing leafy gene produce flowers (therefore fruits) much earlier than normal trees.