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- Author or Editor: Ray A. Bressan x
Obtaining uniform mechano-dwarfing of Arabidopsis thaliana (L.) Heynh. seedlings within dense plantings is problematic. Alternative forms of mechano-stimulation were applied to seedlings in effort to obtain uniform growth reduction compared with undisturbed controls in both greenhouse and controlled growth environments. Arabidopsis grown under low photosynthetic photon flux (PPF) artificial light grew upright with limited leaf expansion, which enhanced mechano-responsiveness compared to that of rosette-growing plants under filtered sunlight or high PPF artificial light. Hypocotyls of seedlings grown at PPFs >60 μmol·m-2·s-1 elongated less and had 6% less sensitivity to mechanical stress than seedlings grown at PPFs <60 μmol·m-2·s-1. Fluorescent lamps alone (F) or fluorescent plus incandescent (F+I) lamps were compared for seedling responses to mechanical stress. Under F lighting, hypocotyl elongation was reduced 25% to 40% by twice-daily brush or plate treatments, and brushed seedlings exhibited more growth reduction than did plate treatments. Seedlings grown under F+I lamps exhibited similar stress-induced growth reduction compared to seedlings grown under F only, but stressed F+I seedlings lodged to a greater extent due to excessive hypocotyl elongation. Temperature-response studies using standardized F-only lighting indicated increased hypocotyl elongation but decreased leaf expansion, and decreased mechano-responsivity to brushing over the temperature range from 20 to 28 °C. Daylength studies indicated similar degrees of mechano-inhibition of hypocotyl elongation over the daylength range of 12, 16, 20, and 24 hours, whereas fresh weight of stressed seedling shoots declined compared to controls. A combination of environmental growth parameters that give repeatable, visual mechanical dwarfing of Arabidopsis include low-PPF fluorescent lighting from 55 to 60 μmol·m-2·s-1, ambient temperatures from 22 to 25 °C, and twice-daily brush treatments.
In vitro-derived shoots of ‘Improved Blaze’ rose (Rosa hybrida L.) were used to investigate the cause of improved root initiation obtained by lowering the concentration of the Murashige and Skoog (MS) salt formulation in the nutrient medium. The number and length of roots per explant increased as the concentration of total nitrogen in the MS salt formulation was reduced from 60 to 7.5 mm. There was no effect on rooting with as much as a 16-fold reduction in the concentration of the remaining MS salts from that of the normal MS formulation, when total nitrogen was kept at a constant 7.5 mm. When nitrogen was maintained at 7.5 mm and the concentrations of the remaining salts were maintained at 1/2 times that of the MS salt formulation, rooting was unaffected by raising the total solute concentration with NaCl to that when the medium contained the full MS nitrogen salt complement. These results show that lowering the total mineral salt level in the nutrient medium provides a more favorable nitrogen salts concentration for rhizogenesis than that provided by the MS salt formulation.
In the paper “Stimulation of Root Initiation from Cultured Rose Shoots through the Use of Reduced Concentrations of Mineral Salts” by Scott E. Hyndman, Paul M. Hasegawa, and Ray A. Bressan (HortScience 17(l):82–83.1982) figures 1 and 2 were mis-positioned on the page. The correct placement of the figures, along with their captions, appears below.
Salinity is a significant limiting factor to agricultural productivity, impacting about 9 × 108 ha of the land surface on the earth, an area about 3 times greater than all of the land that is presently irrigated (17, 18). Reduced productivity occurs as a result of decreased yields on land that is presently cultivated [about one-third of all irrigated land is considered to be affected by salt (18, 45)], as well as due to the restriction of significant agricultural expansion into areas that presently are not cultivated. In the United States, salinity is a major limiting factor to agricultural productivity, and as the quality of irrigation water continues to decline this problem will become more acute (1, 56). About 1.8 million ha of land are salt-affected in California (56), the major agricultural state in the nation. Annual losses to crop production in the salt-affected areas, including the Imperial, Coachella, and San Joaquin valleys, are substantial and are increasing at a significant rate each year (56).
Water availability is one of the principal environmental limitations of crop productivity throughout the world. The water deficits, which are a consequence of either continuous or transitory periods of drought, cause significant yield reductions on presently cultivated land, and greatly restrict the cultivation of crops on over one-third of the earth’s land surface considered to be arid or semiarid (25). These restrictions on yield potential are rapidly becom ing of great concern in the face of the food demands of an ever increasing world population. The problem becomes complicated further by the fact that supplies of suitable irrigation water are dwindling rapidly, and that the costs of irrigation are becoming prohibitive. As a result, studies on the effects of water stress on plant survival and yield are attracting added interest in plant science research.
Crosses and subsequent segregation between inbred lines of ‘National Pickling cucumber (Cucumis satirus L.) resistant to acute exposure to sulfur dioxide, and the sensitive ‘Chipper‘ cucumber indicated that resistance was dominant and may be controlled by a single gene.