Anatomical Alterations Associated with White Fluorescent Light Exposure of Phaseolus vulgaris L. Plants

The biological effect of white fluorescent light exposure (emitted from an ordinary 30 Watt, 220V fluorescent bare lamp) on the anatomical architecture of Phaseolus vulgaris L.plants obtained from pre-treated seeds was obtained . Both soaked and dry seed lots were separately exposed to light source for 1, 2, 3 & 4 discontinuous periods of one hour with a break time of a complete hr. between each two successive periods. Another chronic dose of 4 continuous hrs. of exposure was undertaken. Other control sets of untreated seeds were used for comparison. Cultivation experiment lasted for 50 days ( in plastic pots in the home garden), during which continuous monitoring of the morphological changes were recorded. By the end of the experiment, anatomical studies of roots, stems & leaves of treated plants compared with the untreated ones were undergone.. Roots resulted from soaked seeds, subjected to light for 4 discontinuous hrs.were discriminated by being transformed in shape from normal tap roots to storage roots with distinctive anomalous anatomical features. Advanced secondary thickening with a continuous cylinder of 2ry elements, high lignifications of xylem parenchyma, presence of air cavities in phloem region, presence of phloem fibers, enlarged pith parenchyma and a hollow central cavity were the most conspicuous distinctive features. Plants resulted from 1hr. exposed dry seeds produced a 4-grooved 2ry xylem ring with high lignification and lacked pith. Epidermal cork with variable thicknesses was also a feature of the soaked-seeded exposed plants. Stems of the same T4 soaked treatment were completely lacking 2ry thickening. Metaxylem vessels were also characterized by their narrow diameter and lowered number. Leaves resulted from 3hrs. of exposure (soaked & dry) and the 4hr. exposed soaked seeds were distinguished by their lower values of diversion angle of their leaf blade halves. T3 & T4 soaked-seeded plants had the lowest trichome density, lowest Tpal/Tm value and lowest number of lateral veins (smaller vascular bundles). These features point out to the decreased photosynthetic activity of plants.