Hormonal changes in papaya seedlings subjected to progressive water stress and re-watering

Abstract

Changes on abscisic acid (ABA), jasmonic acid (JA) and indole-3-acetic acid (IAA) levels were investigated in papaya seedlings (Carica papaya L.) cv. ''Baixinho de Santa Amalia'' under progressive water stress and subsequent rehydration. Also, the behaviour of leaf gas exchange and leaf growth was determined under stress condition. The results indicated that ABA and JA differ in their pattern of change under water stress. ABA continuously increased in leaves and roots during the whole period of stress whereas JA showed a sharp increase and a later decrease in both organs. Re-watering reduced rapidly (24 h) leaf and root ABA to control levels whereas the influence on JA levels could not be assessed. Drought and recovery did not alter IAA levels in leaf and root tissues of papaya seedlings. In addition, water stress reduced stomatal conductance, photosynthetic rate, transpiration rate, the percentage of attached leaves and leaf growth. Rehydration reverted in few days the effects of stress on leaf growth and gas exchange parameters. Overall, the data suggest that ABA could be involved in the induction of several progressive responses such as the induction of stomatal closure and leaf abscission to reduce papaya water loss. In addition, the pattern of accumulation of JA is compatible with a triggering signal upstream ABA. The unaltered levels of IAA could suggest a certain adaptive ability of papaya to maintain active physiological processes under progressive drought stress.

Ecophysiology of papaya: a review

“…This damage may chronically reduce the photosynthetic process and delay or even prevent complete re-establishment of photosynthesis after re-irrigation. In contrast, in 'Baixinho de Santa Amália', despite A having been progressively decreased over the course of the dehydrating cycle, reaching 73% of the control after 40 d of water deficit, it fully resumed upon re-hydration (Mahouachi et al, 2007), even though the stress caused leaf drop that began to occur 7 d upon suspending irrigation. Non-hydraulic signals such as abscisic acid (ABA) and jasmonic acid (JA), but not indole-3-acetic acid, differed in their accumulation patterns under stress.…”

“…Whereas ABA continuously increased in leaves and roots during the whole period of stress, JA initially increased and then decreased in both organs. Mahouachi et al (2007) proposed the involvement of ABA as an accumulative, non-hydraulic hormonal signal that could be involved in the induction of several physiological responses in papaya under progressive water stress such as the reduction in gas exchange parameters and leaf abscission.…”

Alterations of Endogenous Hormonal Levels in Plants under Drought and Salinity

“…Despite of these fluctuations, in the literature there are numerous studies showing a JAs endogenous increase under abiotic stresses. For example, JA increased in spear tips of Asparagus officinalis [32], Carica papaya seedlings [33], Pinus pinaster plants [34], Oryza sativa leaves and roots [35] and citrumelo CPB 4475 (a commercial citrus rootstock) [36] exposed to drought. Similarly, under salinity, JA increased in salt-tolerant cv HF tomato from the beginning of salinization, while in salt-sensitive cv Pera it decreased after 24 h of treatment [37].…”

Molecular mechanisms in plant abiotic stress response

“…Recent fi ndings have suggested an interaction between jasmonic acid and ABA in plants under drought stress (Mahouachi et al 2007). The pattern of accumulation of JA is compatible with a triggering signal upstream ABA.…”