Light as a regulator of tissue-cultured plantlet development was investigated by Joan John (Horticulture). She observed that yam plantlet growth and protuber development could be affected by treating the plantlets with EOD R or FR light (John, 1990; John et al., 1993). In more recent work, Sandy Wilson (Horticulture) has been using transgenic tobacco to determine the role of cytokinins in photochrome-regulated plant growth. The transgenic tobacco was transformed to over-produce cytokinins and facilitated measuring cytokinin concentrations in response to EOD R and FR light treatments. Trend analysis of plant responses to EOD light treatments suggests that R light increases cytokinin concentrations in plants (Wilson, 1996).


Manipulation of Low Temperature anf Light Quality for Storage of Broccoli in Vitro

Sandra B. Wilson*, Keiko Iwabuchi, Nihal C. Rajapakse, Department of Horticulture, Clemson University, and Roy E. Young, Department of Agricultural and Biological Engineering, Clemson University, Clemson, SC 29634.

Storage systems for tissue cultured plants offer versatility in managing labor to meet market availability. Storage systems that minimize growth and yet sustain photsynthetic and regrowth potential require temperature, light quality, and light intensity to be manipulated for plantlet growth during and after storage.. Broccoli (Brassica oleracea L. Botrytis Group 'Green Duke') plantlets were cultured photoautotrophically (without sugar) or photomixitrophically (with sugar) on cellulose plugs in liquid medium in vitro for 3 weeks at 23C and 150 µmol m^-2s^-1 photosynthetic photon flux (PPF). To determine the conditions that yield a zero carbon balance, plantlets were subsequently stored for 3 days under different temperatures (1C, 5C, 10C, 15C), different light intensities (1.6 PPF, 4.1 PPF, 8.6 PPF), and different light spectra (white, blue, red). Plantlets stored under 5 PPF and 5C maintained a zero carbon balance. Subsequently, plantlets were stored for 4, 8, or 12 weeks at 5C under darkness or 5 PPF of white, red, or blue light. Stem elongation was observed for plantlets stored under blue light. Plantlets stored under red light were characterized by increased chlorophyll, increased specific leaf mass (leaf dry mass per unit leaf area, SLM), increased starch in leaf tissue, and increased total soluble sugars in leaf and stem tissue. Plantlets grown with sucrose were characterized by increased dry mass, regardless of light treatment. After 8 weeks, plantlets grown with or without sucrose and stored in darkness did not survive acclimatization to greenhouse.