Photosynthetic performance and sucrose metabolism in superior and inferior rice grains with overlapping growth stages under water stress

Abstract

Drought stress at jointing and booting stages of plant development directly affects plant growth and productivity in rice. Jointing and booting stages may overlap in high-latitude areas where water deficits occur. However, little is known about the effects of photosynthesis on grain sucrose metabolism and the differences of sucrose metabolism strategies between superior and inferior grains under different drought stress was unclear. In this study, rice plants were subjected to drought stress for 15 days at jointing-booting. Drought stress affected normal leaf growth, and decreased the leaf area index linearly. Short-term mild drought stress had positive effects on photosynthesis, but long-term drought stress reduced the transpiration rate, stomatal conductance, and intercellular CO₂ concentration. Stomatal conductance increased with drought stress duration but increased intercellular CO₂ concentration did not prevent decrease in net photosynthetic rate. Vacuolar invertase activity was important for panicle development (where its activity differed between superior and inferior grains), but not for rice grain filling. Vacuolar invertase activity of drought-sensitive rice varieties superior grains increased by 111.24%~118.46% under drought stress. Drought stress reduced sucrose-phosphate synthase activities in superior and inferior grains. SuSase activity of inferior grains affected sucrose content significantly.

Keywords: Gradient drought; Jointing-booting stages; Photosynthesis; Sucrose metabolism; Superior and inferior grain.

Fig. 1

Effect of drought stress at booting stage on leaf area index of two rice varieties with overlapping growth stages. A0 and B0, control treatments (0 kPa) of SJ6 and DN425; A1 and B1, mild drought stress treatments (-10 kPa); A2 and B2, moderate drought stress treatments (-25 kPa); A3 and B3, severe drought stress (-40 kPa). Vertical bars represent standard deviation. Values for the same day and the same varieties followed by different letters are significantly different at p = 0.05. Days after drought stress were recorded as Dx days, and days after restoration of irrigation were recorded as Rx days (similarly hereinafter).

Fig. 2

Effect of drought stress at booting stage on leaf SPAD values of two rice varieties with overlapping growth stages.

Fig. 3

Effect of drought stress at booting stage on photosynthetic parameters of two rice varieties with overlapping growth stages. (A, B) Net photosynthetic rate, (C, D) Transpiration rate, (E, F) Stomatal conductance, (G, H) Intercellular CO₂ concentration.

Fig. 4

Effect of drought stress at booting stage on sucrose content in panicles of two rice varieties. *, ** represent significance at p < 0.05 and p < 0.01, respectively. Vertical bars represent standard deviation. Values for the same time and the same variety marked blue is significantly higher than the value marked red (similarly hereinafter).

Fig. 5

Effect of drought stress at booting stage on sucrose synthetase activity in superior (A, B) and inferior (C, D) grain of two rice varieties.

Fig. 6

Effect of drought stress at booting stage on the activity of sucrose phosphate synthetase in superior (A, B) and inferior (C, D) grain of two rice varieties.

Fig. 7

Effect of drought stress at booting stage on vacuolar invertase activity in superior (A, B) and inferior (C, D) grains of two rice varieties.

Fig. 8

Effect of drought stress at booting stage on AGPase activity in superior (A, B) and inferior (C, D) grain of two rice varieties.