| Grain yields in wheat have been increasing at an annual rate approximately 0.9% over the last 30 years (Calderini et al,1999). However,global demand is predicated to increase by 1.6% per year over the next 20 years (Rosengrant,1995). The trend of supply-demand contradiction implied that improvement in yield potential may be meeting this increasing demand. If we consider the whole cereal plant as two parts,leaves and non-leaf organs,then it could be proposed that improvement of wheat yields can be obtained by improving the partitioning of assimilates of non-leaf organs (Frey-Wyssling et al,1959;Sharma-natu et al,1994). Although structure and function of leaves received considerable attention,those of non-leaf organs are poorly documented. In my present study,changes in structure and function of all parts of non-leaf organs (culms,paleae,lemmas,awns,and glumes) were investigated during a series of developmental stages and in various cultivars.Characterization of the culms of lodging-resistant wheat varietiesLodging is a potential cause of yield reduction in cereal crops (Crook et al,1994). In this project,culms of lodging-sensitive and lodging-resistant varieties of wheat (Triticum aestivum L) were compared at the morphological level to determine the anatomical features that are associated with these traits. This analysis revealed that lodging resistant culms are short,possess thicker mechanical tissue,and had larger vascular bundles. Semiquantitative analysis of lignin content in the culm by confocal laser scanning microscopy (CLSM) showed that lignin contents are elevated in lodging-resistant varieties and this together with the anatomical features may provide higher culm strength resulting in increased lodging-resistance. The results from this study were published in Acta Botanica Sinica,42,1258-1262.Characterization of stomatal frequency,stomatal index and guard cell lengthStomatal characteristics appear to be related to variations in net photosynthetic rate and water-use efficiency (Sellers et al,1996). Here,the stomatal frequency,the guard-cell length and the stomatal index of non-leaf organs were investigated comparatively between the ear and the leaf of wheat. The results showed that stomatal frequency of non-leaf organs is significantly lower than that of leaves,whereas the guard-cell length and stomatal index showed different variation patterns in both leaves and non-leaf organs. The average values of the stomatal index in the non-leaf organs in Ca cereals were smaller than those of leaves. Blanke put forward a new physiological process in fruit,'fruit photosynthesis',and featured with lower stomatal frequency (Blanke,1989). The results here also showed that the significant lower stomatal frequency on non-leaf organs,indicating that the new physiological process might exist in these organs of cereals as well. Study results were published in Acta Phytoecologica Sinica,26 (in press).The contributions of non-leaf organs to photosynthesisNext,studies on photosynthetic pigment,the rates of photosynthetic oxygen evolution and 77K fluorescence emission spectrum of awns and lemmas in rice and wheat were carried out. This study demonstrated that the photosynthetic contribution of non-leaf organs was 6% -28% of that of flag leaves. The decline in photosynthetic activity was closely related to the reduction of chloroplast numbers. Interestingly,it was observed that the photosynthetic capacity in the aging plant declined earlier in leaf organs than in non-leaf organs,suggesting that non-leaf organs are still functional in the later development stages,when leaves have been yellowing and exhausted. The relevant results from this part were published in Journal of Chinese Electron Microscopy Society,21,97-101.Changes in chloroplast compositionNon-leaf organs have fewer and smaller chloroplasts than leaves. Glumes and awns are organs directly exposed to light but they contain more grana per chloroplast,bigger granal stacks and more thylakoids per granal stacks and therefore their chloroplasts a...
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