Question

In the pre-lab paper they supplied sucrose to the plants in culture. Could this have affected the plants investment in and reliance on photosynthesis? Discuss in terms of costs and benefits.

I need a full explainatoin on what supplying sugar would do to the plant for the vote.

Answer 1

Sugar and oxygen are the product of plants, in normal condition plants make enough sugar to store, make energy and also it is the main source of carbon, but when they are cultured, plant cells are depressed and external feeding of sugar is required. Sucrose is the most preferred sugar. During the course of sterilization of the medium, sucrose gets hydrolysed to glucose and fructose. The plant cells in culture initially utilize glucose and then fructose. Glucose or fructose can be directly used in the culture media. For energy supply, glucose is as efficient as sucrose while fructose is less efficient and toxic if autoclaved.

Sucrose is an essential part of nutrient medium as an energy source, since most plant cultures are unable to photosynthesize effectively because to poorly developed cellular and tissue development, lack of chlorophyll, inadequate gas exchange and carbon dioxide in tissue culture vessels, they lack auxotrophic capability and need external carbon for energy. Sucrose also supports the maintenance of osmotic potential (osmoticum) and the conservation of water in cells. It has been established that plant tissue cultures do not fix enough CO2 to sustain growth in the absence of sucrose, mainly due to limited CO2 inside the vessel. Though, high sucrose concentration in the media also limits the photosynthetic efficiency of cultured plants by reducing the key enzymes for photosynthesis, levels of chlorophyll.

Mechanism: sucrose transport can either take sucrose by free diffusion where no energy is required or either by H+/Sucrose transports proteins. The energy for this uptake is derived from the pumping of H+ ions across the plasma membrane at the expense of ATP. On the other hand, in some plants the sucrose is broken down into glucose and fructose before the uptake by H+/hexose transporters.

Role of sucrose in plant tissue culture:

• Sucrose is supposed to act as a signalling molecule that initiates/activates starch synthesis.
• Downregulation of CO₂ fixation in photosynthesis.
• Carbohydrate synthesis regulation and its partitioning is regulated by Sucrose (mRNA levels and activity of Sucrose symporters from sugar beet source leaves drastically decreased by Sucrose).
• Sucrose seems to control chlorophyll and non-photosynthetic pigment synthesis, sucrose is known to prevent the chlorophyll pigment accumulation.
• Sucrose is also known to control nitrogen assimilation along with carbon.
• Plant size is increased by the external application of sucrose in wide variety of plants.
• Sucrose may also modify whole plant morphology by regulating the activation of different types of meristems.
• Sucrose promotes branching through the release of dormant axillary buds.
• In seed development, it initiate the end of embryo cell division and increase cell differentiation.
• Averts the oxidative damage.