Abstract
The formation of mature and fertile pollen grains, taking place inside the anther, depends on supply of assimilates, in the form of sucrose, provided mainly by the leaves. Data is limited, however, with respect to the understanding of sucrose metabolism in microspores and the supporting tissues. The aims of the present work were to 1) follow the changes in total and relative concentrations of sucrose, glucose, fructose and starch in the stamen parts and microspores up until anthesis, 2) follow the activities of sucrose-metabolism-related enzymes, in the anther walls fraction and microspores of the crop plant tomato. Sucrose was found to be partially cleaved in the filament, decreasing by more than twofold in the anther wall layers and the locular fluid, and to accumulate in the mature pollen grains, constituting 80% of total soluble sugars. Thus, sucrose was both the starting sugar, supporting microspore development, and the main carbohydrate accumulated at the end of the pollen-development program. The major invertase found to be active in both the anther wall layers and in maturing microspores was cell-wall-bound invertase. High fructokinase 2 and sucrose phosphate synthase activities during pollen maturation coincided with sucrose accumulation. The potential importance of sucrose accumulation during pollen dehydration phase and germination is discussed.
Highlights
The formation of mature and fertile male gametophytes, which takes place inside the anther, depends on assimilates, in the form of sucrose, provided by the leaves [1], with some contribution from the sporophytic tissues of the anther [2,3]
Sucrose was found to be partially cleaved in the filament, decreasing by more than twofold in the anther wall layers and the locular fluid, and to accumulate in the mature pollen grains, constituting 80% of total soluble sugars
Total soluble sugar concentration ranged between 90 and 120 mg·g dry weight (DW)–1 during the tested flower bud developmental stages and was composed of sucrose, glucose and fructose (Figure 1(a)), indicating that sucrose hydrolysis had already begun in this part of the stamen
Summary
The formation of mature and fertile male gametophytes, which takes place inside the anther, depends on assimilates, in the form of sucrose, provided by the leaves [1], with some contribution from the sporophytic tissues of the anther [2,3]. Free microspores from each tetrad is achieved by callase secretion from the tapetal cells, comprising the innermost layer of the anther wall, which nourish the microspores and degenerate thereafter [4,5,6]. At this stage, the incoming sucrose molecules that arrive through the phloem continue to the developing microspores through the anther wall layers and the locular fluid that surrounds the microspores. The same authors suggested that the anther wall tissues may have a buffering function, storing nutrient surplus in starch grains and regulating the availability of soluble sugars in the whole anther
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