Temperatura como estresse abiótico : fisiologia e expressão gênica em cana-de-açúcar

Abstract

Most sugar cane producing states are in dry climate regions, with high summer temperatures.This demonstrates the need to evaluate and develop tolerant cultivars that maintain high productivity. Within this context, it is essential to understand how sugar cane behaves under abiotic stress, especially under different temperatures. With this knowledge, it would be possible to establish genotype selection criteria and then outline strategies for using these sources of tolerance in plant breeding programs. The objective of this study was to evaluate the physiological parameters and the gene expression in the sugar cane cultivar RB86-7515 when submitted to temperatures of 40°C, 28°C and 15°C, at different exposure times of 0, 4, 8, 12, and 24 hours. The design used was a completely randomized design with six replications. The sugar cane plants were kept in a greenhouse until they reached 65 days of growth. They were then submitted to temperature stress in a BOD incubator. Chlorophyll a and b data were obtained, as well as the a / b ratio, together with total chlorophyll and chlorophyll efflorescence. The chlorophyll a fluorescence measurements were made on leaves that were located in the median region of the leaf. The initial (Fo) and the maximum (Fm) fluorescence values were measured. With these variables, the relationships of Fv / Fo and the potential quantum efficiency of photosystem II (FSII) Fv / Fm were estimated. After the Fo and Fm measurements, the photosynthesis induction curve and the fluorescence extinction coefficient analyses were determined. For the evaluation of the gene expression, the leaf tissue samples were submitted to RNA extraction and the determination of the gene expression for the 18S subunit. There were differences between the treatments for the total chlorophyll variables and the chlorophyll a / bratio. For F0, Fm, Fv, Fv / Fm, Fm / F0, and F0 / Fv, the temperatures significantly influenced the determinations. For the results of the gene expression, the genes M6, HSP (sHSP18.2),PER1, and 18S were tested. There were detectable gene activities for 18S at 15°C and 40°C at some of the times.