Discussion
Which of the following statements are TRUE for plant growth regulators?
P. The release of cellulase and polygalacturonase into the cell wall is promoted by abscissic acid
Q. The early biosynthetic steps of gibberellic acid, up to the formation of ent-kaurene take place in the plastid
R. The naturally occurring zeatin belongs to the aromatic group of cytokinins
S. Induction of protease inhibitors as a result of wounding and pathogen attack is activated by jasmonic acid
Answer: B
The true statements are Q, S.
Q is true: gibberellin synthesis begins in the plastid, where geranylgeranyl diphosphate is cyclised to ent-kaurene; the later steps take place in the endoplasmic reticulum and cytosol. S is true: wounding and herbivore attack trigger jasmonic acid signalling, which switches on genes for proteinase inhibitors.
P is false: the release of cellulase and polygalacturonase that dissolves the cell walls in abscission zones is promoted by ethylene, not abscisic acid, despite the latter's name. R is false: zeatin is an isoprenoid (adenine-type) cytokinin; the aromatic cytokinins are a separate group such as benzyladenine. So the pairs with P or R are wrong.
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