'Desiccation tolerance of Rhamnidium elaeocarpum Reissek (Rhamnaceae) seeds

This study aimed to investigate the desiccation tolerance of Rhamnidium elaeocarpum Reissek seeds through physiological and biochemical alterations. Fruit were collected from the municipality of Jaupaci, Goias State, Brazil, when the water content of their seeds had a 37% wet basis (w.b.) and the seeds were subsequently kept in a drying oven with air circulation at a temperature of 35ºC until a water content was reached of 20 to 12% (w.b.). The following parameters were evaluated: germination, germination speed index, emergence, emergence speed index, electrical conductivity and respiration rate. Furthermore, the electrophoretic profile of the isoenzymes: catalase, peroxidase and esterase, the enzymatic activities of endo-β-mannanase and α-amylase and the electrophoretic analysis of heat-resistant proteins were performed. A higher germination speed and respiratory rate was obtained for seeds with a water content of 12% w.b., and the activity of catalase isoforms was more pronounced in seeds with a higher degree of dehydration, which was in contrast to peroxidase, showed decreased activity. The seeds contained heat-resistant proteins of low molecular weight that ranged from 48.7 to 13.2 kDa. We found that the acquisition of drying tolerance in R. Elaeocarpum Reissek seeds is associated more with catalase than with esterase and peroxidase.

本研究旨在通过生理与生化变化，探讨巴西果（Rhamnidium elaeocarpum Reissek）种子的耐脱水性。试验所用果实采自巴西戈亚斯州尧帕西（Jaupaci）市的植株，采集时其种子含水量以湿基（wet basis, w.b.）计为37%；随后将种子置于温度35℃的通风干燥箱中进行脱水处理，直至含水量降至20%至12%（w.b.）。本研究测定的指标包括：发芽率、发芽速度指数、出苗率、出苗速度指数、电导率以及呼吸速率。此外，本研究还开展了过氧化氢酶（catalase）、过氧化物酶（peroxidase）与酯酶（esterase）等同工酶的电泳谱型分析，内切-β-甘露聚糖酶（endo-β-mannanase）及α-淀粉酶（α-amylase）的酶活性测定，以及耐热蛋白的电泳分析。结果显示，当种子含水量为12%湿基时，其发芽速度与呼吸速率均达到更高水平；脱水程度更高的种子中，过氧化氢酶同工酶的活性更为突出，这与过氧化物酶的变化趋势截然相反——后者的活性呈下降态势。供试种子含有分子量介于13.2 kDa至48.7 kDa之间的小分子耐热蛋白。本研究结果表明，巴西果（Rhamnidium elaeocarpum Reissek）种子的耐脱水性获得与过氧化氢酶的关联度显著高于其与酯酶和过氧化物酶的关联度。