The Study of Hexose Transporters Role in Determining Sink Strength of Tomato Fruits at Ripening Stage

An organ or tissue that produces more than its metabolic and growth needs and can export photosynthetic assimilates is considered as a source. The sinks are the consumers of photosynthetic materials, such as root, stem, meristems, and growing fruits. The sink strength is the competitive ability of a sink organ to attract assimilates and consists of sink size and sink activity. Sink size is a physical parameter that is determined by the cell numbers and cell size, whereas sink activity is a physiological parameter that is determined by many processes such as carbon metabolism, assimilate transport, and storage by the sink cells. To examine the physiological role of hexose transporters in determining the sink strength of individual fruits at the ripening stage, the regulation of hexose transporters gene expression and concentrations of glucose, fructose, and sucrose were studied when the sink/source ratio was altered in two cultivars of greenhouse tomato consist of ‘Grandella’ and ‘Isabella’ under the greenhouse condition. To this end, four sink/source ratios were applied: saving one fruit per truss (۱F), two fruits per truss (۲F), three fruits per truss (۳F), and no fruit pruning (control). The results showed that fruit thinning could increase glucose, fructose, and sucrose concentrations in the fruits. It could also modulate the expression of tomato hexose transporter genes (LeHT۱, LeHT۲, and LeHT۳). The availability of mobile assimilate to a particular sink may be determined by competition among sink organs, and based on the results of the present study, applying fruit thinning and limiting the number of fruits per truss, decreased competition in the truss and had a positive effect on the sink strength of individual fruit per truss, with considering the increased trend of LeHTs expression level by increasing sink strength, so we can conclude hexose transporters participate in determining sink strength at ripening stage of tomato fruits.

Keywords:

Fructose , Glucose , Sink-source balance , Sucrose