Changes of sucrose metabolism in leaf subtending to cotton boll under cool temperature due to late planting

Because reproductive growth could be influenced by sucrose metabolism of major source leaf (leaf subtending to cotton boll, LSCB), we hypothesized that decreased temperatures under field conditions would limit morphology and biomass distributions of the whole cotton plant by decreasing photosynthesis of LSCB and inhibiting sucrose metabolism in LSCB. To address this hypothesis, two cotton cultivars, Kemian 1 and Sumian 15, were grown at three planting dates (25 April, 25 May and 10 June) in 2009–2011 to obtain LSCB and bolls exposed to contrasting ambient temperatures while at the same developmental stage (white flowers on the first position of 6–7th fruiting branches). Sample collection and measurement were conducted during boll development at MDTmin of 25.9 °C and 24.0 °C for the early planting date of 25 April (optimal planting date in the Yangtze River Valley), 20.4 °C and 18.4 °C for the 25 May planting date, and 16.5 °C and 16.0 °C for the 10 June planting date in 2010 and 2011, respectively. Microclimate measurements included photosynthetic active radiation, relative humidity and air temperature. Late planting decreased boll number, boll weight, LAI, total biomass and harvest index (P < 0.05), but increased leaf to shoot, leaf to stem and leaf to boll ratios. Cool temperature increased SLW and carbohydrate contents in LSCB, but decreased Pn and sucrose transformation rate in LSCB (P < 0.05). Under cool temperatures (MDTmin of 20.4 °C and 16.5 °C in 2010, and 18.4 °C and 16.0 °C in 2011 during boll development) in the late planting dates (25 May and/or 10 June), the activities of Rubisco and cytosolic fructose-1,6-bisphosphatase (cy-FBPase) increased, whereas sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities decreased, and their peak values were delayed. The variability of Pn, SPS activity, sucrose transformation rate in LSCB and boll weight under cool temperature for Sumian 15 was greater than those of Kemian 1. In addition, there was a significantly positive correlation between Pn and SPS in LSCB, as well as SPS and boll weight in 2010 and 2011 (P < 0.05). It is concluded that, of the measured physiological and reproductive processes, the difference of sucrose metabolizing enzymes in LSCB for the two cotton cultivars under cool temperature due to late planting were mainly determined by SPS activity, while higher Pn and SPS in LSCB were necessary to improve boll weight. However, greater boll weight does not necessarily need high Pn, SPS and SuSy activities, and great sucrose transformation rate in LSCB.

► Under cool temperature due to late planting, the morphology and biomass distributions in whole cotton plant were analyzed, and the sucrose metabolism dynamics in LSCB during boll development.
► The two cultivars were Kemian 1 (tolerant to temperature) and Sumian 15 (sensitive to temperature).
► Under cool temperature, the difference of sucrose metabolism in LSCB for the two cotton cultivars were mainly determined by SPS activity.
► Higher Pn and SPS activity in LSCB were favorable to great boll weight.