Poster: Temperature responses

Abs # 138: The Effect of Night Chilling on Photosynthesis for Cotton.

Presenter:	Singh, Bir , birsingh@yahoo.com
Authors	Singh, Bir  (A)   Haley, Luke  (A)   Nightengale, Jamie  (A)   Haigler, Candace  (B)   Holaday, Scott  (A)
Affiliations:	(A): Texas Tech University (B): North Carolina State University

The aim of this study was to determine the effects of long-term night chilling on photosynthesis for cotton, Gossypium hirsutum cv. coker-312. Cotton plants overproducing spinach sucrose phosphate synthase (SPS) were included to determine whether enhanced capacity to synthesize sucrose would alter the response of photosynthesis to night chilling. Growth at 28/10 ⁰C (day/night) caused no reduction in A measured at ambient (37 Pa) or elevated (220 Pa) CO₂ for young stem leaves of seedlings of any genotype (wildtype, SPS+, and segregating nulls) relative to A for leaves grown at 28/24 ⁰C. Also, growth with cool nights tended to maintain A at saturating CO₂ for stem leaves 5 weeks old for all genotypes. Cool nights resulted in higher values of A at ambient and saturating CO₂ for sympodial leaves subtending a boll 25-30 days post anthesis, suggesting the possibility of increased carbohydrate supply with cool nights from the sympodial leaves to the bolls during the day. However, no genotypic differences in A were noted within a growth regime. The impact of cool night temperatures on maximum RuBP saturated rate of carboxylation (V_cmax), electron transport driving regeneration of RuBP (J_max), triose-phosphate utilization (V_TPU) and carbohydrate partitioning will be discussed. Interestingly, growth with cool nights resulted in a substantial reduction (10-45%) in the total extractable SPS (V_max) activity in all leaf types of wildtype and segregating null plants, but not for leaves of SPS+ plants. These data suggest that enhancing extractable SPS activity does not have an effect, per se, on the response of photosynthesis to night chilling. Supported by a grant from the Texas Advanced Technology Program.