Study of morphological and histological changes in melon plants grown from seeds irradiated with UV-B

Abstract: It is well known that exposure of plant seedlings or plants to UV-B radiation induces changes in gene expression resulting in biochemical and morphological modifications. However, there is little information on the effects and potential utility of irradiation of seeds with UV-B. The aim of this study was to apply UV-B radiation in melon seeds using various irradiation times and then assess the effect on growth and morphology of the plant. Seeds of cultivar ‘Topmark’ were exposed to UV irradiation with wavelength centered at 302 nm, for periods of 0, 15, 30 and 45 minutes (UV dosages of 0, 99, 198 and 297 mJ cm^-2, respectively). The irradiated seeds were seeded in a mixture of peat moss and perlite for greenhouse germination. Morphological parameters such as plant height, stem diameter, number of leaves, leaf area, fresh and dry weights were evaluated. Stomatal frequency, stomatal index, and length and width of stomata were studied. Histological analyses were conducted to determine the areas of the stem vascular bundle and xylem vessels, width and length of vascular bundles, and the area of the lumen of xylem vessels. The analysis of variance indicated significant differences between treatments, with the treatment of 15 minutes (99 mJ cm^-2) of seed exposure to UV-B radiation generating 24.87 and 32.42 % more fresh and dry weight of the plants, respectively. Stomatal index was augmented on the adaxial surface by 52.26, 7.14 and 13.55 %, in the treatments of 99, 198 and 297 mJ cm^-2, respectively, in contrast with the control treatment, while the length of stomata was increased by 6.99% in the treatment with 30 minutes exposure time (198 mJ cm^-2). Stomatal frequency was unchanged by exposure to radiation. The irradiation of the seeds caused decrease in P, Ca and Na in the leaves of plants.