Yagi K J, Konz K G, Stay B, Tobe S S
Department of Zoology, University of Toronto, Ontario, Canada.
Gen Comp Endocrinol. 1991 Feb;81(2):284-94. doi: 10.1016/0016-6480(91)90013-v.
The regulation of juvenile hormone III (JH III) biosynthesis and release by the corpora allata (CA) was studied in penultimate and final instar male and female larvae of Diploptera punctata using an in vitro radiochemical assay. Final instar female CA produced JH III (2 to 6 pmol.hr-1 per pair) only during the first 8 days of the 20-day stadium, but produced and released farnesoic acid (FA), a JH III precursor, (0.5 to 2.0 pmol.hr-1 per pair), during the entire stadium. FA was identified by cochromatography on TLC of both the product from CA incubations with [3H]FA standard as well as by esterification of biosynthesized FA to methyl farnesoate (MF). Biosynthesis of MF and JH III acid occurred at less than 0.25 and less than 2 pmol.hr-1 per pair, respectively. Because regression analysis of the time course of JH III release over 6 hr showed a constant rate of release after a lag period lasting up to 1.7 hr, rates of JH release of untreated CA (spontaneous) and FA-treated CA (stimulated) were determined by 2-hr sequential incubations of CA, following a 2-hr preincubation. FA-treated rates of JH III release were higher than spontaneous rates. In penultimate instars, the decline in the spontaneous rates during the latter half of the stadium was accompanied by a reduced degree of FA stimulation. In final instars, as the spontaneous rates declined between Days 2 and 6, the magnitude of the stimulation of JH III biosynthesis by FA increased, whereas in the second half of the stadium, the degree of stimulation was very low. Addition of exogenous FA to CA from late final instars increased FA production significantly more than JH III production. This apparent stimulation of FA biosynthesis is evident in CA with both high and low spontaneous rates of JH release and suggests that rate limitation of JH III biosynthesis in the final stadium occurs in part at the level of the o-methyl transferase which converts FA into MF.
利用体外放射化学分析法，研究了点刻原臭虫末龄前和末龄雄雌幼虫中咽侧体（CA）对保幼激素III（JH III）生物合成和释放的调节作用。末龄雌虫的CA仅在20天龄期的前8天产生JH III（每对2至6 pmol·小时⁻¹），但在整个龄期都产生并释放法尼酸（FA），一种JH III前体，（每对0.5至2.0 pmol·小时⁻¹）。通过将CA孵育产物与[³H]FA标准品在薄层色谱上共色谱分析以及将生物合成的FA酯化生成法尼酸甲酯（MF），鉴定出了FA。MF和JH III酸的生物合成分别以每对小于0.25和小于2 pmol·小时⁻¹的速率发生。由于对6小时内JH III释放时间进程的回归分析表明，在长达1.7小时的滞后期后释放速率恒定，因此在2小时预孵育后，通过对CA进行2小时连续孵育来测定未处理CA（自发）和FA处理CA（受刺激）的JH释放速率。FA处理后的JH III释放速率高于自发速率。在末龄前幼虫中，龄期后半段自发速率的下降伴随着FA刺激程度的降低。在末龄幼虫中，随着第2天至第6天自发速率的下降，FA对JH III生物合成的刺激程度增加，而在龄期后半段，刺激程度非常低。向末龄后期的CA中添加外源FA，FA产量的增加明显超过JH III产量。这种对FA生物合成的明显刺激在JH释放自发速率高和低的CA中均很明显，表明末龄期JH III生物合成的速率限制部分发生在将FA转化为MF的邻甲基转移酶水平。
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