Anatomical features of pepper plants (Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light

Pepper plants (Capsicum annuum L. cv., Hungarian Wax) were grown under metal halide (MH) lamps or light-emitting diode (LED) arrays with different spectra to determine the effects of light quality on plant anatomy of leaves and stems. One LED (660) array supplied 99% red light at 660 nm (25 nm band-width at half-peak height) and 1% far-red light between 700-800 nm. A second LED (660/735) array supplied 83% red light al 660 nm and 17% far-red light al 735 nm (25 nm band-width at half-peak height). A third LED (660/blue) array supplied 98% red light at 660 nm, 1% blue light between 350-550 nm, and 1% far-red light between 700-800 nm. Control plants were grown under broad-spectrum metal halide lamps. Plants were grown at a mean photon flux (300-800 nm) of 330 mu mol m(-2) s(-1) under a 12 h day-night photoperiod. Significant anatomical changes in stem and leaf morphologies were observed in plants grown under the LED arrays compared to plants grown under the broad-spectrum MH lamp. Cross-sectional areas of pepper stems, thickness of secondary xylem, numbers of intraxylary phloem bundles in the periphery of stem pith tissues, leaf thickness, numbers of chloroplasts per palisade mesophyll cell, and thickness of palisade and spongy mesophyll tissues were greatest in peppers grown under MH lamps, intermediate in plants grown under the 660/blue LED array, and lowest in peppers grown under the 660 or 660/735 LED arrays. Most anatomical features of pepper stems and leaves were similar among plants grown under 660 or 660/735 LED arrays. The effects of spectral quality on anatomical changes in stem and leaf tissues of peppers generally were correlated to the amount of blue light present in the primary light source. (C) 1997 Annals of Botany Company.