Hypocotyl elongation, effect

As shown by measurement of root and hypocotyl elongation, the treatment with the RO fraction did not prevent the initial absorption of water by the seed, which is essentially a passive process. However, it effectively inhibited the ensuing expansion of these organs, which results from a combination of cell expansion and cell division. As late as 46 h after seed imbibition, no sign of cell division was visible in roots from seeds treated with 1 8- and 1 10-diluted RO fraction, and only occasional divisions, mainly in the procambial area, were observed after treatment at 1 14 dilution. By contrast, control roots resumed active cell division within 16 h after imbibition. As a conspicuous consequence of the inhibition of cell expansion/division activity, the apex of roots from treated seeds appeared distinctly... 

Adventitious Root Formation. IAA stimulates adventitious root formation in cucumber hypocotyl cuttings (28). On the other hand, BR has either no effect or is slightly inhibitory, while it stimulates hypocotyl elongation. Gibberellin is usually inhibitory. However, it has been reported that in mung bean cuttings, the formation of root primordia was not inhibited (29). 

A fungal product termed KM-01 retards the promoting effects of brassinolide on rice lamina bending and radish hypocotyl elongation, but nothing is known about the mode of action [85]. 

Another compound with plant hormone-like activity is raphanusanin, a natural inhibitor of radish hypocotyl elongation which is believed to be instrumental in its phototropic response [179]. Raphanusanin has been reported to prevent auxin-induced MT reorientations [19]. However, there is no direct evidence that raphanusanin exerts an effect on MTs. 

To investigate the biosynthetic steps affected by brassinazole, we examined the effect of biosynthetic intermediates downstream from cathasterone on hypocotyl elongation of brassinazole-treated Arabidopsis [9]. The feeding experiment suggests that the target(s) of brassinazole could be the two-step conversion of... 

Table 5.2. The effect of D. ajacisDitcrpenoid Alkaloids on Normal and Gibberellic Acids (GAs)—Induced Cucumber Hypocotyl Elongation [Courtesy of Lawrence and Waller (1973a,b, 1975)]...

Lercari, B. and Sodi, E, Photomorphogenic responses to UV radiation. II A comparative study of UV effects on hypocotyl elongation in a wild-type and an aurea mutant of tomato (Lycopersicon esculentum Mill), Photochem. Photobiol, 56, 651,1992. 

Table VI. Time-course Study of the Effects of Chondrillasterol on Germination and Hypocotyl and Radicle Elongation in Mung Beans...

Figure 1. Effects of CaCl2 on bioassays for auxin, gibberellin, and cytokinin. A effects of CaCl2 on elongation of oat coleoptile sections in the presence and absence of indoleactic acid B effects on elongation of lettuce hypocotyls in the presence and absence of gibberellic add and C effects on enlargement of Xanthium cotyledon pieces in the presence and absence of benzyladenine (13).

Treatment of the roots of tomato and radish plants with BR led to elongation of the petioles and hypocotyls, and treatment of the bases of mung bean hypocotyl cuttings led to the elongation of the epicotyls (46,47,48). In cucumber hypocotyl segments, washing with water reduced the effect of BR treatment (49), and the uptake of BR has been studied in detail in maize roots, where it accumulated independently of energy supply and 30% was irreversibly bound (50). 

N,N -Dicyclohexylcarbodiimide (DCCD), an inhibitor of membrane bound ATPase, has been shown to strongly inhibit IAA-induced elongation of cucumber hypocotyl sections, while it has no effect on GA-induced elongation (36). DCCD markedly inhibits BR-induced elongation (8), suggesting that BR acts differently from GA, but similarly to IAA in this particular case. 

Both stem cell elongation and xylem differentiation are auxin-mediated processes. There has long been speculation that BRs act through alterations in the auxin response [109]. This is certainly not always the case, as BR induces elongation of soybean hypocotyls without activating any of the auxin-induced genes such as the SAUR genes [112]. On the other hand, one of the effects of BR in tomato hypocotyls appears to be to increase the sensitivity of the tissue to auxin [113]. Thus some BR effects may actually be mediated via auxin, while others are independent of auxin. 

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