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Major advisor Dr. S.D. Upadhyaya

Presented byJitendra Singh Painkra

M.Sc. (Ag.) Final yearRoll No - 5989

Physiological and molecular control of sink activity, partitioning efficiency and harvest index

Department of Plant physiologyJawaharlal Nehru Krishi Vishwa Vidyalaya, Jabalpur (M.P.)

INTRODUCTION

Source:- A source of organic material is a region in which organic

materials are synthesised. Example:- leaf ,root, tuber, or tuber during development.

Sinks:-Any non-photosynthetic organ or an organ that does not

produce enough photosynthate to meets its own needs.Example:- root, seed, fruit, root tuber and tuber during developing.

Fruit stores photoassimilate

Leaf makes photoassimilate

Source and sink relationship

Define the terms source and sink in relation to the transportation of organic molecules in the phloem of plants.

SOURCE SINK

Translocation

Feedback inhibition

Source = Photosynthesis (PS)Sink = Growth and development

Multiple sources and sinks

Examples:Beta maritime (wild beet) root is a sink during the first growing season. In the second season the root becomes a source, sugars are mobilized and used to produce a new shoot. In contrast, in cultivated sugar beets roots are sinks during all phases of development.

Translocation

Source

Source

Source

Sink

Sink

Sink

SinkSink

Sink

Developing apex

Translocation of sucrose can be in any direction – depending on source and sink location and strength.The flow of water in plants is almost always from roots to leaves.

Loading and unloading in phloem

1.Phloem loading is through the sucrose–H+ symporters

Sucrose from mesophyll cell to apoplast, then to SE/CC into sieve element.

Requirement for energy and against concentration of sucrose.

This autoradiograph shows that labeled sugar moves from the apoplast into sieve elements and companion cells against its concentration gradient in sugar beet (Beta vulgaris) . Label accumulates in the small veins, sieve elements, and companion cells of the source leaf, indicating the ability of these cells to transport sucrose against its concentration gradient. (From Fondy 1975, courtesy of D.Gieger

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(2) Phloem unloading :-

Pathways for phloem unloading. The sieve

element companion cell complex (CC/SE) is considered a

single functional unit. The presence of plasmodesmata is

assumed to provide functional symplastic continuity. An

absence of plasmodesmata between cells indicates an

apoplastic transport step

Cont..

Physiological and molecular control of sink and source activity

Besides transport of photosynthates from one part to another phloem is also involved in transport of signal molecules.

Signal between source and sink might be physical (such as turgor pressure) or chemical (such as hormones and carbohydrates).

Signals indicate turgor change could be transmitted rapidly via interconnecting systems of sieve elements.

Thus not only in sucrose in phloem, but sucrose or its metabolites can act as signals that modify the activities of source and sink.

Harvest index

useful terms used to describes portioning to dry matter by the plant are biological yield and economical yield.

The term biological yield was proposed by Nichiporovich (1960) the total dry matter accumulation of a plants system.

The proportion of biological yield represented by economic yield has been called the harvest index.

The coefficient of effectiveness, or the migration coefficient

All these terms characterize the movement of dry matter to the harvested part of the plant.

Cont..

Crop yield can be increased either by increasing the total dry matter produced in the field or by increase the proportion of economic yield (the harvest index or both )

There is potential for increasing yields by both method In Oat (Takeda and Frey 1976) a large genetic population showed variability in both biological yield and harvest index.

The harvest index, the most widely used term, is defined as fallows:-

Economic yield Harvest index = ×100 Biological yield 

Oat line with high biological yield and harvest index of 40- 50% showed the highest grain yield.

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Yield components

Grain yield is a product of a number of subfraction called yield component and can be expressed as follow:-

Y= Nr Ng Wg

Where Y= Grain yield

Nr = The number of reproductive unit (e.g. head ears,

panicles ) per unit of ground area.

Ng = The number of grains per reproductive unit.

Wg = The average weight per Grain. Yield components are affected by management, genotype,

and environment, which often helps explain why a reduction in yield occurred.

The genotype can influence emergence capability and set the potential for tillering, flower number, number of flowers, that develop into grain amount assimilate produced and assimilate partitioning.

The environment affects the ability of the plant of express its genetic potential.

Water, nutrients, temperature, light, and other environmental factor at levels other than optimum can reduced one or more yield components.

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Conclusion

FACE studies show that the crop yields at [CO2] projected for 2050 are enhanced by an average 18% with the current cultivars tested and ~30% with the most responsive hybrid rice cultivars.

In order to achieve 50% increase in crop yield by the middle of 21st century, photosynthetic radiation use efficiency need to be substantially improved.

Both the source activity and the sink strength will need to be coordinately enhanced to maximize net photosynthesis and yield.

Assimilate move to sinks, where the of sugar in the apoplast around the causes sugar and water move the phloem.

For high yield, the should quickly produce enough leaf area index to intercept most of the light for maximum dry matter production, after which it should maintain high light interception and should partitioning in the largest quantities possible to the organs of economic value without affecting quality of harvest ability.

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