Chilling effects on leaf photosynthesis and seed yields of Phaseolus vulgaris

Abstract

Three common bean cultivars (climbing ‘Negro Mecentral’, bushlike ‘Negro Mecentral’, and ‘Tendergreen’) were studied during seed maturity. A single dark period of a chilling treatment (4 °C, 12 h) resulted in a sizeable reduction of the photochemical and photosynthetic activities of the leaves during the seed maturity stage. Leaf net photosynthesis, transpiration rate, and stomatal conductance for water vapor were drastically reduced in ‘Tendergreen’ at 28 days after anthesis, but in bushlike ‘Negro Mecentral’ these values decreased until 30 days after anthesis. Chilling drastically reduced electron transport of freshly lysed chloroplasts isolated from bushlike ‘Negro Mecentral’ and ‘Tendergreen’ at 32 days after anthesis. This contrasts with climbing ‘Negro Mecentral’ plants, in which electron transport decreased progressively between 28 and 32 days after anthesis. Photophosphorylation rates at 32 days after anthesis were reduced by 31, 58, and 45% in climbing ‘Negro Mecentral’, bushlike ‘Negro Mecentral’, and ‘Tendergreen’ plants, respectively. Light-dependent proton uptake was more damaged in ‘Tendergreen’ (88%) at 32 days after anthesis than in bushlike ‘Negro Mecentral’ (31%) and climbing ‘Negro Mecentral’ (38%). Seed yield per plant tended to decrease with treatment in climbing ‘Negro Mecentral’ (45% at 32 days after anthesis) and in bushlike ‘Negro Mecentral’ (34% at 32 days after anthesis), whereas in ‘Tendergreen’ the yield apparently was not affected. However, seed weight and size of climbing ‘Negro Mecentral’ decreased following the treatment, while they increased in bushlike ‘Negro Mecentral’ and ‘Tendergreen’. Seed protein content increased dramatically at 28, 30, and 32 days after anthesis in treated bushlike ‘Negro Mecentral’ (52, 78, and 42%, respectively), but it did not change in climbing ‘Negro Mecentral’ and ‘Tendergreen’. In conclusion, the chilling effects on photochemical activities, seed yield, and seed composition of common bean plants at seed maturity vary according to cultivar and plant developmental stage. Key words: Phaseolus vulgaris, photosynthesis, chilling effect.