Different leaf surface characteristics of three grape cultivars affect leaf optical properties as measured with fibre optics: possible implication instress tolerance

Young leaves of three grape cultivars having different surface characterist ics (cv. Athiri, pubescent; cv. Soultanina, glabrous green; and cv Fraoula, glabrous red-brown) only during the early stages of their development, wer e used to investigate the potential, differential effect of a trichome laye r or a pigmented epidermis on the light microenvironment within the mesophy ll. The penetration of forward propagated 310, 360 and 430 nm radiation int o the leaf tissues was monitored using a quartz fibre-optic microprobe. The mesophyll of the young leaves of Athiri was much better protected from ult raviolet-A, ultraviolet-B and high visible radiation compared to the other two cultivars. Abaxial, as well as adaxial trichome layers attenuated almos t all incident radiation at 310 nm and 360 nm and a considerable part of th e blue light (430 nm). No significant differences in light attenuation from epidermal and mesophyll layers between the other two cultivars were observ ed. The adaxial epidermis of young and dehaired leaves of cv. Athiri was la rgely ineffective in absorbing the incident ultraviolet-B radiation. In add ition, the dehaired lamina of such leaves exhibited 80% lower relative conc entration of ultraviolet-absorbing compounds per leaf surface area, compare d to leaves of similar ontogenetic stage in the cv. Soultanina. It is propo sed that the occurrence of a dense trichome layer in young leaves, besides other proposed functions, may pray a protective role against not only ultra violet radiation damage, but also against high insolation. This protection could be advantageous under stress conditions during leaf development.