when competing against normal plants, silenced plants produced more above-ground biomass and berries. Upon herbivory, systemin was down-regulated in black nightshade in contrast to the other peptides which are up-regulated after herbivory. By contrast HypSys were up-regulated and activated the synthesis of protease inhibitors. The down-regulation of systemin was associated with increased root mass but did not decrease shoot mass, demonstrating that systemin can cause developmental changes as a result of herbivory, allowing the plant to tolerate, rather than directly resist attack. Tomato roots were also affected by tomato systemin, with root growth increasing at high tomato systemin concentrations. By allocating more resources to the roots, plants under attack are thought to store carbon and then use it to re-grow when the attack ends. Overexpressing AtPEP1 also increased root and shoot biomass in A. thaliana. Abiotic stress resistance Overexpression of systemin and HypSys has been found to improve plants' tolerance to abiotic stress, including salt stress and UV radiation. When prosystemin was over-expressed in tomato, transgenic plants had lower stomatal conductance than normal plants. When grown in salt solutions, transgenic plants had higher stomatal conductances, lower leaf concentrations of abscisic acid and proline and a higher biomass. These findings suggest that systemin either allowed the plants to adapt to salt stress more efficiently or that they perceived a less stressful environment. Similarly, wounded tomato plants were less susceptible to salt stress than unwounded plants. This may be because wounding decreases the growth of the plant and therefore slows the uptake of toxic ions into the roots. An analysis of salt-induced changes in gene expression found that the differences measured between the transgenic and normal plants could not be accounted for by changes in conventional salt stress-induced pathways. Instead Orsini et al. suggested that the activation of the jasmonic acid pathway determines a physiological state that not only directs resources towards the production of compounds active against pests, but also pre-adapts plants to minimize water loss. These effects are achieved by negatively regulating the production of hormones and metabolites that will force plants to invest additional resources to counteract water loss, a secondary effect of herbivores. Plants grown under UVB light are more resistant to insect herbivory compared with plants grown under filters that exclude the radiation. When tomato plants are exposed to a pulse of UVB radiation and then weakly wounded, PIs accumulate throughout the plant. By themselves, neither the