Shenggen He

The effects of host defence elicitors on betacyanin accumulation in Amaranthus mangostanus seedlings

The effect of elicitors associated with host defence on betacyanin accumulation in Amaranthus mangostanus seedlings was investigated. Under the conditions of the experiments, betacyanin accumulation was generally enhanced by light. Methyl jasmonate (MeJA) treatment increased betacyanin synthesis in a concentration-dependent response. Seedlings treated with ethylene as 5mM Ethephon also had elevated levels of betacyanin. In contrast, salicylic acid (SA) and H(2)O(2) treatments had no influence on betacyanin contents in light or dark. Combined MeJA with Ethephon or H(2)O(2) had an additive effect on betacyanin accumulation in dark-grown seedlings. However, a decline was recorded in light-grown seedlings. Moreover, an antagonistic effect on betacyanin synthesis was found when MeJA and SA were added simultaneously. Our results indicate that betacyanin content in A. mangostanus seedlings can be upregulated by MeJA and ethylene. Both additive and antagonistic effects in regulating betacyanin synthesis in A. mangostanus seedlings were observed between MeJA and other elicitors.

Two phenylalanine ammonia-lyase genes (DcPAL2 and DcPAL3) are involved in the cut-induced stem-end wound reaction of carnation (Dianthus caryophyllus L.)

Summary The cut stem-end wound reaction is potentially important during the physical blockage of water uptake in cut flowers. Phenylalanine ammonia-lyase (PAL; EC 4.3.1.24) is involved in plant wound reactions, being the key regulatory enzyme of phenylpropanoid metabolism. Two full-length PAL genes (DcPAL2 and DcPAL3) cDNAs were isolated from cut carnation (Dianthus caryophyllus L.) flower stem-ends and found to be transiently expressed following wounding. DcPAL2 was 2,439 bp-long with an open reading frame (ORF) encoding a putative protein of 718 amino acids. DcPAL3 was 2,453 bp-long with an ORF encoding a putative protein of 709 amino acids. An increase in PAL enzyme activity within the basal 2-cm stem-end of cut carnation flowers commenced 12 h after wounding and peaked at 48 h. However, DcPAL2 and DcPAL3 transcript levels increased earlier than PAL activity. DcPAL2 transcript levels increased gradually to a peak 12 h after wounding and remained relatively high thereafter. In contrast, DcPAL3 gene transcripts peaked 3 h after wounding, then decreased. A third PAL gene, DcPAL1, showed constitutively high levels of expression, with only a slight change after wounding. Collectively, these results suggest that expression of DcPAL2 and DcPAL3 leads to increased PAL activity during the wound reaction in cut carnation stems.

Diurnal and seasonal changes in the xylem water potentials of Grevillea and Myoporum plants during drought

Summary Drought is an irregular feature of World climate and has adverse effects on ornamental plants growing in urban environments. Grevillea ‘Moonlight’ and Myoporum elipticum are attractive native Australian species that are commonly used in parks and gardens and are generally regarded as being drought-tolerant. Diurnal and seasonal water relations during a drought cycle of G. ‘Moonlight’ and M. elipticum, growing together in a non-irrigated garden bed, were monitored during a Summer (wetter)-to-Winter (dryer) transition period using a pressure chamber. G. ‘Moonlight’ generally maintained higher xylem water potentials than M. elipticum. Pre-dawn xylem water potentials in drought-affected M. elipticum dropped to around –2.5 MPa, while G. ‘Moonlight’ maintained pre-dawn xylem water potentials of around –1.0 MPa. This difference suggests that, because pre-dawn xylem water potentials reflect soil water potentials, G. ‘Moonlight’ accessed a different or additional source of soil water to M. elipticum. This study demonstrates the utility of the pressure chamber for describing the diurnal and seasonal water relations of ornamentals in a mixed planting in urban horticulture.