Spectral quality of supplemental LED grow light permanently alters stomatal functioning and chilling tolerance in basil ( Ocimum basilicum L.)

The spectral qualities of light contain environmental information used by plants as cues to modify their biology in order to adapt and survive. LED based lamps, with their highly definable spectral properties, thus hold great perspectives for use in greenhouse production. The effects of the spectral qualities of light on plant physiology is still not fully understood, and a great fraction of the current knowledge further comes from studies looking at short term effects or using monochromatic light treatments in enclosed growth chambers, thus far from the light conditions of greenhouse production. The objective of this study was to determine whether spectral modifications to the supplemental LED lighting in greenhouse production could modify post-cultivation performance of basil, which is prone to chilling injuries (CI). We cultivated basil under greenhouse conditions using four different supplemental LED light treatments; 80%Red/20%Blue, 80%Red/20%Blue + UV-A, 40%Red/60%Blue and 80%Red/20%Green, followed by a post-cultivation shelf life simulation including a chilling treatment. Stomatal anatomical features and levels of hormonal regulators, abscisic acid (ABA) and ABA glucosylester (ABA-GE), along with soluble sugars, fatty acids and lipoxygenase activity (LOX) were determined at the end of the growing period. Without compromising grow rates, the light treatments showed marked effects on the chilling tolerance and shelf life performance with increasing ratios of blue light having negative effects, and green light having positive effects on chilling tolerance. Differences in shelf life performance seemed mediated solely by factors related to stomatal functioning. Stomatal density (number of stomata per leaf area, SD) increased with increasing ratios of blue light whereas green light showed indications to decrease SD. [ABA] and [ABA-GE] showed positive correlation to SD, whereas the ratio of [ABA-GE]/[ABA] conversely correlated negatively with increased SD. Our results thus suggest an important relationship between leaf water retention and post-cultivation chiling tolerance in basil.