Effect of Drought Stress during Soybean R2–R6 Growth Stages on Sucrose Metabolism in Leaf and Seed

Abstract

Sucrose is the main photosynthesis product of plants and the fundamental carbon skeleton monomer and energy supply for seed formation and development. Drought stress induces decreased photosynthetic carbon assimilation capacity, and seriously affects seed weight in soybean. However, little is known about the relationship between decreases in soybean seed yield and disruption of sucrose metabolism and transport balance in leaves and seeds during the reproductive stages of crop growth. Three soybean cultivars with similar growth periods, “Shennong17”, “Shennong8”, and “Shennong12”, were subjected to drought stress during reproductive growth for 45 days. Drought stress significantly reduced leaf photosynthetic rate, shoot biomass, and seed weight by 63.93, 33.53, and 41.65%, respectively. Drought stress increased soluble sugar contents, the activities of sucrose phosphate synthase, sucrose synthase, and acid invertase enzymes, and up-regulated the expression levels of GmSPS1, GmSuSy2, and GmA-INV, but decreased starch content by 15.13% in leaves. Drought stress decreased the contents of starch, fructose, and glucose in seeds during the late seed filling stages, while it induced sucrose accumulation, which resulted in a decreased hexose-to-sucrose ratio. In developing seeds, the activities of sucrose synthesis and degradation enzymes, the expression levels of genes related to metabolism, and the expression levels of sucrose transporter genes were enhanced during early seed development under drought stress; however, under prolonged drought stress, all of them decreased. These results demonstrated that drought stress enhances the capacity for unloading sucrose into seeds and activated sucrose metabolism during early seed development. At the middle and late seed filling stages, sucrose flow from leaves to seeds was diminished, and the balance of sucrose metabolism was impaired in seeds, resulting in seed mass reduction. The different regulation strategies in sucrose allocation, metabolism, and transport during different seed development stages may be one of the physiological mechanisms for soybean plants to resist drought stress.

Leaf Soluble Sugars and Free Amino Acids as Important Components of Abscisic Acid—Mediated Drought Response in Tomato

“…In this way, the accumulation of sucrose in sink tissues increases, resulting in a decreased hexose-to-sucrose ratio. In addition, drought stress increases the expression and the activities of acid invertase enzymes in the leaves, leading to irreversible hydrolysis into glucose and fructose [ 59 , 60 ].…”

Sucrose Utilization for Improved Crop Yields: A Review Article

“…Plants subjected to drought stress usually have accumulated soluble sugars, including sucrose, stored in their source leaves ( Figure 3 ). The accumulation of this stored sucrose in the source leaves act as an imperative energy derivative strategy which improves plant tolerance to drought stress condition [ 142 ]. Interestingly, sucrose could also be accumulated in the leaves if there is a low demand for sucrose at the sink cell [ 136 ].…”

“…This is an indication of increased capacity of sucrose unloading into seeds and activation of sucrose metabolism during the early seed developmental stage under a drought-stress condition [ 138 ]. However, during late seed-filling stages, basipetal sucrose flow from source leaves to seed decreased, leading to an impaired supply of seed (sink) metabolic need, and thus reduced seed weight or yield [ 142 ]. Since these transporters trigger sucrose export from source leaves to the root (sink), especially during the early plant-developmental stage, enhancing sucrose transport to the root is promising to optimize root development under drought stress [ 138 ].…”

Response of Soybean Lines to Drought Stress During Reproductive Phase

“…Water stress reduced number of full pods per plant by 6.3%, seed yield/plant by 12.8%, and seed size by 6.3% (Table 3). Du et al [13] found that drought prevailing during generative stage, mainly at the middle and late seed filling phases, sucrose movement from leaves to seeds was lessen, and the balance of sucrose metabolism was defected in seeds, rendering in seed mass reduction. Number of full pods per plant and seed size are main attributes of soybean seed yield, the higher the number and the larger the seed size, the higher the yield [14,15,16].…”