Jongyun Kim

Physiological and molecular responses to drought in Petunia: the importance of stress severity

Plant responses to drought stress vary depending on the severity of stress and the stage of drought progression. To improve the understanding of such responses, the leaf physiology, abscisic acid (ABA) concentration, and expression of genes associated with ABA metabolism and signalling were investigated in Petunia × hybrida. Plants were exposed to different specific substrate water contents (θ = 0.10, 0.20, 0.30, or 0.40 m3·m–3) to induce varying levels of drought stress. Plant responses were investigated both during the drying period (θ decreased to the θ thresholds) and while those threshold θ were maintained. Stomatal conductance (gs) and net photosynthesis (A) decreased with decreasing midday leaf water potential (Ψleaf). Leaf ABA concentration increased with decreasing midday Ψleaf and was negatively correlated with gs (r = –0.92). Despite the increase in leaf ABA concentration under drought, no significant effects on the expression of ABA biosynthesis genes were observed. However, the ABA catabolism-related gene CYP707A2 was downregulated, primarily in plants under severe drought (θ = 0.10 m3∙m–3), suggesting a decrease in ABA catabolism under severe drought. Expression of phospholipase Dα (PLDα), involved in regulating stomatal responses to ABA, was enhanced under drought during the drying phase, but there was no relationship between PLDα expression and midday Ψleaf after the θ thresholds had been reached. The results show that drought response of plants depends on the severity of drought stress and the phase of drought progression.

Slowly developing drought stress increases photosynthetic acclimation of Catharanthus roseus.

Our understanding of plant responses to drought has improved over the decades. However, the importance of the rate of drought imposition on the response is still poorly understood. To test the importance of the rate at which drought stress develops, whole-plant photosynthesis (P(net) ), respiration (R(dark) ), daily carbon gain (DCG), daily evapotranspiration (DET) and water use efficiency (WUE) of vinca (Catharanthus roseus), subjected to different drought imposition rates, were investigated. We controlled the rate at which the substrate dried out with an automated irrigation system that allowed pot weight to decrease gradually throughout the drying period. Fast, intermediate and slow drying treatments reached their final pot weight [500 g, substrate water content (θ) ≈ 0.10 m³ m(-3) ] after 3.1, 6.6 and 10 days, respectively. Although all drying treatments decreased P(net) and R(dark) , slow drying reduced P(net) and R(dark) less than fast drying. At a θ < 0.10 m³ m(-3) , DCG and DET in the slow drying treatment were reduced by ≈50%, whereas DCG and DET in the fast drying treatment were reduced by 85 and 70% at a θ of 0.16 m(3) m(-3) . Plants exposed to slow drought imposition maintained a high WUE, even at θ < 0.10 m³ m(-3) . Overall, physiological responses to low θ were less severe in plants subjected to slow drying as compared with fast drying, even though the final θ was lower for plants exposed to slow drying. This suggests that the rate at which drought stress develops has important implications for the level of acclimation that occurs.

Classification of Korean Chrysanthemum species based on volatile compounds using cluster analysis and principal component analysis

In the analysis of chemotype relationship among Korean Chrysanthemum species, the volatile compounds in the leaves of 15 taxa were analyzed and identified by gas chromatograph/mass spectrometry. Principal component analysis and cluster analysis used for the grouping based on the volatile compounds. Fifteen taxa of Charysanthemum species were categorized into three groups. Groups I and II included higher ketones than Group III. Group I had five C. zawadskii subspecies: acutilobum, acutilobum var. tenuisectum, acutilobum var. alpinum, lucidum, and coreanum. Five C. zawadskii subspecies were analyzed with main volatile compounds of D-limonene and m-thymol. Group II consisted of four C. zawadskii subspecies including naktongense, yezoense, latilobum, and latilobum var. leiophyllum, and one species C. makinoi. They consisted of main compounds of linalool, cis-chrysanthenol, eugenol, and chrysanthenone. Group III included five C. indicum species and related species: C. indicum, var. albescens, var. acuta, C. boreale, and C. lineare. The present study was able to classify volatile compounds of Korean Chrysanthemum species attributable to major compounds, such as hydrocarbons (sabinene, cymene, β-selinene), alcohols (1-octen-3-ol, cis-chrysanthenol, hinesol), ketones (chrysanthenone, camphor), and esters (cis-sabiene hydrate, trans-chrysanthenyl acetate).