Low-temperature Storage of Micropropagated Broccoli Plantlets under Varying Light Quality

Abstract

Micropropagation is often associated with mass production at a competitive price. Since labor accounts for a large portion of micropropagation costs, alternative measures to distribute labor costs are necessary. One such method of distributing labor costs is the use of storage systems to hold micropropagated plantlets until market availability. Broccoli (Brassica oleracea L. `Green Duke') plantlets were cultured photoautotrophically (without sugar) or photomixotrophically (with sugar) on cellulose plugs in liquid media in vitro for 3 weeks at 23 °C and 150 μmol·m–2·s–1 photosynthetic photon flux (PPF). To determine the conditions that yield a zero carbon balance, plantlets were subsequently stored for 3 d under different temperatures (1, 5, 10, 15 °C), different light intensities (1.6, 4.1, 8.6 PPF), and different light spectra (provided by white or blue fluorescent bulbs or red Light Emitting Diodes). Plantlets under 3 PPF and 1 °C maintained a zero carbon balance. Subsequently, plantlets were stored for 4, 8, or 12 weeks at 1 °C under darkness or 3 PPF of white, red, or blue light. Prior to low temperature storage, photomixotrophic plantlets were characterized by increased chlorophyll, dry mass, total soluble sugars (TSS), leaf starch, and net photosynthetic rate (NPR). Illumination during storage was necessary to maintain dry mass, TSS, NPR, and regrowth potential of photoautotrophic plantlets. When sucrose was provided to the media, dark stored plantlets survived up to 12 weeks of storage. During storage, the quality of broccoli plantlets was best maintained under red light. Red light increased chlorophyll, TSS, and dry matter accumulation into leaves during storage. In addition, photoautotrophic plantlets stored for 8 or 12 weeks under red light had higher survival rates once acclimatized to the greenhouse when compared to photoautotrophic plantlets stored in darkness or under white or blue light.