Injured plants produce jasmonates, inhibit cell division and stunt growth
It is well known that plants growing under unfavorable conditions are generally smaller than those growing under unstressed conditions: indeed, it is estimated that in the United States, abiotic stress reduces the yield of agricultural crops by 22 % on average.
A dramatic example of the effect of stress – in this case, repeated injury – on plant growth is given by bonsai trees, in which every aspect of their stature, including height, circumference and leaf size, is uniformly reduced to as little as 5% of that of their untreated sister trees. However, the mechanism of wound-induced growth retardation remains obscure.
Plant growth results from the division of “stem cells” in the apical meristems located at the very end of the green shoots and roots. Shoot tips are not only tiny (0.1–0.3 mm in diameter), but are normally hidden from view by very young leaves emerging from the base of the meristem. Thus, initial leaf growth and shape is by cell division, and more than 90% of leaf growth is by subsequent cell expansion.
Yi Zhang and John Turner of the University of East Anglia found that when the leaves of the model plant Arabidopsis are injured, cell division in the apical meristem is reduced, plant growth is arrested within days, and new leaves only grow at one. half their normal size although leaf cell size is not affected.
Unexpectedly, cell division suppression in the apical meristem occurs through a signaling pathway initiated by the wound hormone, jasmonate, which is synthesized in damaged mature leaves. Arabidopsis mutant lines unable to synthesize or respond to jasmonate are not only taller than normal plants, but their growth is not reduced by the stress of injury.
The researchers note that this finding opens up the possibility of enhancing crop growth through manipulation of the jasmonate signal pathway.
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