Respiration and Carbon Partitioning. Thomas G Chastain CROP 200 Crop Ecology and Morphology

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1 Respiration and Carbon Partitioning Thomas G Chastain CROP 200 Crop Ecology and Morphology

2 Respiration Aerobic respiration is the controlled oxidation of reduced carbon substrates such as a carbohydrate to CO 2 and H 2 O. This oxidation not only provides energy for plant metabolic processes but also provides the essential building blocks for crop growth and development. In the plant, respiration provides energy for crop growth and development. O 2 CH 2 O CO 2 + H 2 O + ATP Reduced Carbon Oxidized Carbon Chemical energy

3 Respiration Respiration takes place in the mitochondria and glyoxysomes, specialized organelles, and in the cellular cytoplasm. Membranes in the mitochondria divide the organelle into four compartments. Oxidative phosphorylation (electron transfer) takes place along the inner membrane. The matrix contains the citric acid cycle enzymes. Mitochondrial structure

4 Respiration Aerobic respiration is an oxygen-requiring process and for the aerial portions of the plant, oxygen is not limited except in times of flooding. The soil atmosphere on the other hand, limits the aerobic respiration that can take place in the plant s root system. O 2 concentration decreases with increasing depth in the soil profile whereas CO 2 increases with depth.

5 Respiration Overview of Respiration and Carbohydrate Metabolism

6 Carbon Partitioning Partitioning is the preferential distribution of photosynthetic products, known as photoassimilates, to various parts of the plant, including the components of yield. Photoassimilates serve as substrates for growth and development, and respiration. Source is the site of carbon production or storage. Mature leaves and some stems are sources. Sink is the site of utilization of carbon. Carbon in the form of photoassimilates moves from sources to sinks. Young leaves, fruits and seeds, buds, and roots are sinks they import carbon to support growth and metabolic activity.

7 Carbon Partitioning Translocation is the process of moving carbon to storage organs, other sinks, and to provide these for the nonphotosynthetic parts of the plant. Xylem movement is acropetal and unidirectional from the roots in the transpiration stream. Phloem movement is bi-directional (basipetal or acropetal). Transport form Sucrose is the most important transport form for the translocation of carbon. Others include raffinose and stachyose (important in many dicots), mannitol, and sorbitol. Sucrose

Sucrose Unloading (dpm %) Carbon Partitioning Growth activity is greatest along the stem where sucrose (carbon) unloading from the phloem is greatest.

8 Sucrose Unloading (dpm %) Carbon Partitioning Growth activity is greatest along the stem where sucrose (carbon) unloading from the phloem is greatest Sucrose Unloading Growth Growth Rate (mm h- 1 x100) Stem position from apex (mm) Sucrose unloading and growth rate in pea stem tissue. Pea leaf and stem

Age of tiller affects carbon export from the mainstem to tillers.

9 Labeld Carbon Carbon Partitioning Tiller 40 Roots Young Tillers Crown The crown is the part of the plant where the shoot system (tillers) meets the roots. Age of tiller affects carbon export from the mainstem to tillers. Older tillers are independent of the mainstem while younger tillers are not independent and require carbon from the mainstem for their development Tiller Weight (mg) Old Tillers

10 Carbon Partitioning Some organs are used for carbon storage for later growth and development of the plant or for grain filling. Carbon storage organs include seeds, stem bases, roots, rhizomes, tuber, etc. Leaves are a site of temporary storage. Starch storage takes place in the chloroplast for later mobilization. Starch is usually broken down and moved out of the chloroplast at night. Sucrose can also be stored in leaves. Storage is used to supply carbon for regrowth of forage crops after defoliation. If plants are defoliated too often without replenishment of stored carbon, then plants may die or suffer from reduced productivity. Potato tuber

11 Carbon Partitioning Assimilated carbon is delivered to the tuber via the phloem as sucrose and is carbon substrate for starch synthesis and storage in the tuber. Maximum tuber number is reached prior to maximum tuber weight. Tubers are first formed and then filled, primarily with starch amylose or amylopectin. Amylopectin

12 Photosynthesis in leaf canopy Source Translocation of sucrose through stem Sinks Starch synthesis and storage in tubers

13 Carbon Partitioning Sucrose is not transported far from the phloem before it is converted to starch. Storage parenchyma cells are the site of starch storage in the tuber. Tuber growth ceases once all available cells in the tuber have expanded and are filled with starch. Starch synthesis continues until the end of tuber growth and generally declines with the supply of photoassimilates.

Sink activity of developing seeds is much greater than that of vegetative tissues Panicle Translocation

14 Carbon Partitioning Carbon moves from sources (flag leaf, stem, parts of the inflorescence) to seeds (sink). The primary transport form for carbon translocation to seed from the canopy is sucrose. Sink activity of developing seeds is much greater than that of vegetative tissues Panicle Translocation of sucrose through stem Starch synthesis and storage in seed Stem Flag leaf Sucrose Photosynthesis in leaf canopy

15 Carbon Partitioning Sucrose concentration in grass seed declines as the seed matures. Starch concentrations increase until they reach about 1/3 of the total weight of the seed. Maximum starch concentration is reached before minimum sucrose concentration is attained. Therefore, seed filling in grasses is limited more by sink size restrictions rather than source materials.

Translocation 11/30/2010. Translocation is the transport of products of photosynthesis, mainly sugars, from mature leaves to areas of growth and

Translocation 11/30/2010. Translocation is the transport of products of photosynthesis, mainly sugars, from mature leaves to areas of growth and Translocation Translocation is the transport of products of photosynthesis, mainly sugars, from mature leaves to areas of growth and storage. Phloem is the tissue through which translocation occurs. Sieve