Efffect Of Abiotic Stress On Mobilization From The Stem

Mass balance, that is calculating the amount of stem loss in weight during grain filling compared to the amount of grain weight gain, appears to vary with cultivars, with stress, and with manipulation of the source supply or sink demand (14, 15, 23, 26). Some cultivars may lose two or three times as much mass as other cultivars (14, 15). In one report (15) the stem loss of TNC (Total Non-structural Carbohydrate) contributed 25% to the weight of the ear in one cultivar and 9.4% in a second cultivar. Heat stress increased the calculated percent contribution to 34.5% in the first cultivar and 16.7% in the second cultivar (15). Leaf chlorophyll loss during heat stress was positively correlated with the capacity to store reserves in the stem, which could later be mobilized for grain filling (23). Reducing leaf area by 25% at anthesis decreases the leaf contribution of carbon to the grain, but had no influence on mass per grain an affect attributed to the ability of the stem to remobilize stored reserves buffering the decrease in leaf contribution (25). The stem can also increase storage acting to buffer the loss of sink demand when spikelets are removed, so there is no feed back inhibition of photosynthesis by a lack of grains to fill (22, 26). Altering source supply by shading during grain fill suggests that 80-93% of kernel weight can be provided by pre-anthesis stored reserves (16). Moisture can also affect the remobilization of stored reserves (19). Plastic mulch, which alters soil moisture content, increased vegetative dry matter accumulation by 26% at anthesis, produced 36% more grain and remobilized more dry matter to the grains after anthesis when compared to non-mulched wheat (19). The second internode below the head contributed the greatest percentage of vegetative loss in weight during kernel dry matter accumulation (19). Research using mass balance has suggested that the amount of stored reserves, most of which is fructan although this is often not documented, mobilized to the grain depends on cultivar and on environmental conditions during grain fill.

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