Responses to low temperature stress in phaseolus species

Expansion of common bean (Phaseolus vulgaris L.) crops in the northern Great Planes has been hampered due to the lack of cultivars demonstrating sufficient vitality under low temperature conditions. Phaseolus angustissimus L., a wild bean species, has been previously shown to possess the ability to survive low temperatures in field trials. Freezing tolerance experiments under controlled conditions resulted in P. angustissimus demonstrating a greater capacity for freezing tolerance than P. vulgaris, as all P. vulgaris plants studied were dead at -2.5oC while most P. angustissimus plants treated to the same conditions survived. Exposure to chilling temperatures over five days resulted in stunted growth in both species, but the cultivated bean suffered more compared to the wild bean, as noted by a marked loss in tissue water content over the first three days of chilling. Interspecific macroarray hybridizations of a cDNA library from cold acclimated Medicago sativa L. using cDNAs derived from non-chilled and three-day chilled P. vulgaris and P. angustissimus plants showed that P. vulgaris showed more changes in gene expression after three days of chilling. Also, P. vulgaris showed a general trend towards down-regulation of the transcripts sampled on the third day of chilling compared to P. angustissimus. RT-PCR experiments were conducted using cDNAs from plant tissues exposed to various durations of chilling to confirm the results from the macroarray experiment. These time-course RT-PCR experiments revealed expression patterns across various chilling durations in genes identified from the macroarray. Data from these experiments suggest that P. vulgaris and P. angustissimus seedlings respond differently to low temperature exposure, and that some of the changes in P. angustissimus transcripts monitored here may be useful for researchers in better understanding how Phaseolus species can respond better to chilling temperatures