Abstract
Plants can react to environmental stresses through the abscission of infected, damaged, or senescent organs. A possible mode of action of methyl jasmonate (JA-Me) to induce the formation of the secondary abscission zone (SAZ) in the stems of Bryophyllum calycinum was investigated concerning plant hormone dynamics. Internode segments were prepared mainly from the second or third internode from the top of plants with active elongation. JA-Me applied to the middle of internode segments induced the SAZ formation above and below the treatment after 5–7 days. At 6 to 7 days after JA-Me treatment, the above and below internode pieces adjacent to the SAZ were excised and subjected to comprehensive analyses of plant hormones. The endogenous levels of auxin-related compounds between both sides adjacent to the SAZ were quite different. No differences were observed in the level of jasmonic acid (JA), but the contents of 12-oxo-phytodienoic acid (OPDA), a precursor of JA, and N-jasmonyl-leucine (JA-Leu) substantially decreased on the JA-Me side. Almost no effects of JA-Me on the dynamics of other plant hormones (cytokinins, abscisic acid, and gibberellins) were observed. Similar JA-Me effects on plant hormones and morphology were observed in the last internode of the decapitated growing plants. These suggest that the application of JA-Me induces the SAZ in the internode of B. calycinum by affecting endogenous levels of auxin- and jasmonate-related compounds.
Highlights
Plants encounter plentiful biotic and abiotic stresses, leading to shedding of no longer needed or damaged organs such as leaves, branches, flowers, and fruits, from the parent plants
To clarify jasmonic acid (JA)-Me’s possible mode of action to induce the formation of the secondary abscission zone (SAZ) in terms of its plant hormone dynamics, we focused on differences in plant hormone dynamics between adjacent tissues to the SAZ induced by JA-Me in stem segments, as well as decapitated growing plants of B. calycinum
The contents of IAN and indole-3-carboxylic acid (ICA) were lower in the senescent than in the non-senescent side (Figure 2). These results suggest that the SAZ formation induced by JA-Me is closely related to the modification of indole-3-acetic acid (IAA) biosynthetic pathways via IAM, IAN, and ICA from tryptophan
Summary
Plants encounter plentiful biotic and abiotic stresses, leading to shedding (separation) of no longer needed or damaged organs such as leaves, branches, flowers, and fruits, from the parent plants. This process is known as abscission, and it is strongly associated with plant growth and development [1,2,3,4,5,6,7,8,9]. In response to tissue injury or infection, differentiation of abscission zones in abnormal positions on stems, petioles, pedicles, and branches, designated as the secondary abscission zone (SAZ), can occur in vivo [1,16]. The secondary abscission has been observed primarily in various in vitro systems involving pedicels of Malus sylvestris [17] and Pyrus communis [18], stems of Impatiens sultani [10,11,19], Morus alba [20], Citrus sinensis [21], and Phaseolus vulgaris [16], and petiole explants of P. vulgaris [22], Pisum sativum pedicle, or Euphorbia pulcherrima flower [23]
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