Water‐deficit accumulates sugars by starch degradation—not by de novo synthesis—in white clover leaves (Trifolium repens)

Abstract

Labeling 13CO2 in steady-state condition was used to estimate quantitative mobilization of recently fixed carbon or stored sugar during water-deficit in white clover (Trifolium repens L.). Water-deficient gradually decreased leaf-water parameters and total amount of recently fixed carbon. Amount of 13C incorporated into glucose, sucrose and soluble sugars fraction rapidly decreased after 3 days of water-deficit treatment. In contrast, the previously stored soluble sugars significantly increased after 5 days of water-deficit with a coincidence of significant decrease in starch concentration. A highly significant (P < or = 0.001) relationship between the decrease in leaf-water potential caused by water-deficit and the increase in ratio of soluble sugar/starch concentration was observed in water deficit-stressed plants. The data indicate that soluble carbohydrate accumulated by water-deficit treatment is mainly because of the hydrolysis of previously stored starch rather than to de novo synthesis.

Effect of Se application on photosynthesis, osmolytes and water relations in two durum wheat (Triticum durum L.) genotypes under drought stress

“…Here the changes in the concentration patterns of nonstructural carbohydrates in the leaves may indicate that under drought conditions soluble sugars accumulated at the expense of starch. It has been also reported that accumulated soluble sugars in white clover under drought were mainly derived from degradation of stored starch rather than a result of de novo synthesis (Lee et al, 2008). Se treatment increased concentration of soluble sugars in both leaves and roots of well-watered and drought-stressed plants particularly in 'Saji'.…”

“…In contrast, leaf starch content was lowered by water deficit. Drought-induced accumulation of soluble sugars is a well-known response in plants that is either the result of increased partitioning of photoassimilates to the synthesis of free sugars and/or enhanced starch degradation (Lee et al, 2008). Here the changes in the concentration patterns of nonstructural carbohydrates in the leaves may indicate that under drought conditions soluble sugars accumulated at the expense of starch.…”

Lignification in Relation to the Influence of Water-deficit Stress in Brassica napus

“…In previous researches in white clover, it has been established that drought results in an inhibition of de novo protein synthesis (Kim et al, 2004;Lee et al, 2005), which in turn leads to a transient amino acid accumulation (Lee et al, 2005) and an increase in ammonia and compatible solutes such as soluble sugars and proline (Lee et al, 2005;Lee et al, 2008a). The increased proline loading to phloem caused by drought has significance on the down-regulation of N uptake and the assimilation of newly absorbed N with decreasing nitrate reductase activity in roots (Lee et al, 2009a).…”

“…Moreover, in many higher plants under drought stressed condition, the alteration of carbohydrate metabolism in response to drought stress has been reported (Souza et al, 2004). Drought results in an increase of soluble carbohydrate pool and this accumulation is mainly due to the hydrolysis of previously stored starch rather than to de novo synthesis (Lee et al, 2008a). The accumulation of sugars would be involved in dehydration tolerance by protecting the macromolecules through the maintenance of s sufficient degree of hydration during water loss (Sánchez et al, 2004 (Lee et al, 2009b).…”

“…This suggestion would be associated with a transient accumulation of amino acids and soluble carbohydrates only for the early period (Lee et al, 2005;Lee et al, 2008a) when the crops are exposed to mild water deficit stress. However, it has been well documented that severe drought stress is responsible for the increase in cell wall lignification (Katerji et al, 1997).…”