Effect of Light Quality on Growth and Free Indoleacetic Acid Content in Phaseolus vulgaris.

Early work on the effects of light quality on plant elongation produced many conflicting reports. Vince et al. (15) pointed out that this could be due to the use of ill-defined wave band limits and unequal energy levels. Conflict still exists, how-ever, in spite of improvedl techniques. Vince and Stoughton (16) have reported that interno(le elongation is more dependent on the species than on other factors, while Meijer (13) observed that liglht intensity Nas the determining factor. In a study conducte(d with a number of species he found(l that at lowr intensities red lighlt is more inhiihitorv to eloingation than is blue. His observations have been confirnme(d by Fortanier (5), who pointe(l out further that results obtained with low intensities are opposite to those obtaine(d with high intensities. In hiis studlies wN-itlh ghlerkin see(dlings M\eijer (13) foun(d that applicatioln of synthletic auxins produced elongation in plalnts inhihited by re(d light. This effect was reversed b1 the application of antiauxins. From these findings he conclu(led that IAA is involved in the effect of lighlt on plant elongationi. Blaauw-Jansen (1) aind( Briggs (3) have shown that red light lowvers the level of IAA or auxin-like substances presenit in plants. Thalt IAA can be photooxidized bh blue light in the presence of riboflavin was dcemonstrated bv Galstoni (6). Hillman and Galston (9) reportedl that the activity of IAA oxidlase was indluctivelv inhihbited b1 redl light. The inhibition was reversible bh near infrared radiation. Although Meijer (13) found that exposure to far-red light resulted in greater levels of IAA than exposure to redl, hiis observations are not necessarilv incomiipatible with Hillman's and Galston's, for both destructioni all)( production of IAA mayr be affected. Conflicting aii( insufficieiit evidence has iiia(le it impossible to dleci(le conclusively whether IAA plays a role in the inihihition of plant growtlh hy redl light, although Heatlh andl Vince in a recent reviewv (8) of the subject Nere temipted to coniclude that IAA is not involved in this particular phenomen,on. In the present study, further data on this questioln wrere obtained through investigation of the relationships betwveen