Plant Organization: Leaf development

Organization Organization in plants is dependent upon programmed, controlled cell division, followed by growth, further cell division and ultimately, differentiation. Programmed and controlled cell division occurs within the domain of the vegetative apex. Leaves also follow a programmed development process

the apex All the tissues within the apex differentiate rapidly. By about 150 µm, cells within the apical region are starting to differentiate. In the pine apex (above), you can see developing leaflets. The Coleus apex to the right, shows rapidly developing leaflets beneath the apical dome.

internal organization adaxial epidermis palisade mesophyll vascular bundles spongy mesophyll stomata

leaf development these form the epidermis and associated structures marginal two types of initials submarginal The diagrams which illustrate the development of the leaf were inspired by those that appear in ‘Plant Anatomy’ 2nd Ed. by Katherine Esau 1953: Library of Congress Catalogue card number: 65-12713. New York : John Wiley,  581.4 ESA    and especially Fig. 16.6 on page 455. The Leaf chapters are highly recommended as a basis for further study these form mesophyll as well as the procambial and cambial tissue

how organized? epidermal, mesophyll and vascular tissues are organized and develop in specific ways. What is the control mechanism?

structural & functional tissue dermal non- vascular vascular dermal

two meristems marginal sub marginal

deriving procambium marginal sub marginal procambium

Esau’s developmental outline upper epidermis palisade parenchyma bundle sheath procambium Vascular bundles MI SI bundle sheath The diagram above, illustrates (but not necessarily the strict sequence) the steps involved in a typical mesomorphic dicotyledonous leaf. The diagram can be modified to accommodate all leaf forms – including those in which the bundle sheath surrounds a mestome sheath which may enclose the underlying vascular tissue entirely or partially. You are encouraged to read the following articles which deal with the ontogeny of the mestome sheath. Dengler, N.G., Dengler, R. and Hattersley, P.W. (1985) Differing in ontogenetic origins of PCR ("Kranz") sheaths in leaf blades of C4 grasses (Poaceae). Amer. J. Bot. 72, 284-302.( Soros, C. and Dengler, N. (2001) Ontogenetic Derivation and Cell Differentiation in Photosynthetic Tissues of C3 and C4 Cyperaceae. American Journal of Botany 88 (6):992-1005. Kawamitsu, Y., Hakoyama, S., Agata, W. and Takeda, T. (1985) Leaf interveinal distances corresponding to anatomical types in grasses. Plant Cell Physiol. 26, 589-593. middle spongy parenchyma lower spongy parenchyma lower epidermis see notes below

no middle spongy layer? upper epidermis palisade parenchyma bundle sheath MI SI procambium vascular bundles bundle sheath lower spongy parenchyma lower epidermis

add a mestome sheath upper epidermis palisade parenchyma bundle sheath SI The mestome sheath is derived from the procambium, and forms the outermost layer of the vascular bundle. The mestome sheath may become lignified at maturity, and will normally contain a high frequency of plasmodesmata at the outer bundle sheath, and to the inner vascular parenchyma cells. Useful references: Dengler, N.G., Dengler, R. and Hatterley, P.W. (1985) Differing in ontogenetic origins of PCR ("Kranz") sheaths in leaf blades of C4 grasses (Poaceae). Amer. J. Bot. 72, 284-302. Dengler, N. and Kang, J. (2001) Vascular patterning and leaf shape. Current Opinion in Plant Biology 4, 50-56. procambium vascular bundles mestome sheath bundle sheath lower spongy parenchyma Notes lower epidermis