Abstract
Paclobutrazol (PBZ) has been associated with effects on the photosynthetic capacity of plants. PBZ affects the growth and development of plants in general. However, little is known about the effects of PBZ on photosynthetic performance and related anatomical features of herbaceous peony (Paeonia lactiflora Pall.) leaves. In the present study, PBZ application resulted in a significant reduction in peony plant height. Furthermore, PBZ application significantly increased photosynthetic rate (Pn), transpiration rate (Tr) and water use efficiency (WUE), but significantly decreased intercellular CO2 concentration (Ci) at some stages from the bolting stage to the bud stage of the plants, compared to controls. Moreover, PBZ application increased the maximum quantum yield of PSII photochemistry (Fv/Fm), coefficient of photochemical quenching (qP) and intrinsic PSII efficiency (ΦPSII), but decreased the coefficient of non-photochemical quenching (qN) and non-photochemical quenching (NPQ). Leaves treated with PBZ had a heavy aggregation of chloroplasts close to the cell wall, with distinct grana lamellae, more and bigger starch grains (on average for a chloroplast), and fewer plastoglobuli, as compared to the control. PBZ increased chlorophyll content (SPAD) and the number of chloroplasts in individual cells in the foliar ultrastructure. PBZ-treated leaves had a darker green color with decreased luminosity (L*) and increased hue angle (h°). The results indicated that plants treated with PBZ were superior in terms of increased photosynthetic characteristics when compared with untreated controls. The direct cause of the increase in Pn and leaf greenness of PBZ-treated P. lactiflora may be the increase in chlorophyll content.
Highlights
Herbaceous peony (Paeonia lactiflora Pall.) is one of the most popular traditional flowers used in China, and has more than 400 years of cultivation history
Stages correspond to 4 consecutive weeks as S1, S2, S3 and S4 from bolting to bud development of peony plants; z Treatment; y Leaf traits were chlorophyll a (Chla), chlorophyll b (Chlb), total chlorophyll (Chl), SPAD value (SPAD), and color coefficients:: L *: luminosity; a *: red and green properties; b *: yellow and blue properties; c *: chroma; h◦ : hue angle; x Mean ± standard error
Stages correspond to 4 consecutive weeks as S1 (Stage 1), S2 (Stages 2), S3 (Stages 3) and S4 (Stages 4) from bolting to bud development of peony plants; y Treatment; x Chlorophyll fluorescence parameters were the maximum quantum yield of PSII photochemistry (Fv/Fm), coefficient of photochemical quenching, coefficient of non-photochemical quenching, intrinsic PSII efficiency (ΦPSII ) and non-photochemical quenching (NPQ); w Mean ± standard error
Summary
Herbaceous peony (Paeonia lactiflora Pall.) is one of the most popular traditional flowers used in China, and has more than 400 years of cultivation history. PBZ application has reduced plant height, improved stem diameter and leaf. There is an important need to improve the quality of peony for outdoor cultivation and increase various types of growth indicators through PBZ application. This would promote the commercialization of peony production in China and elsewhere. Previous investigations have indicated that PBZ application has improved photosynthetic capacity of crop plants [9]. The photosynthetic capacity of plants is closely correlated to many kinds of growth indices. It has been proven that improving photosynthetic capacity can increase quantity and quality of flowers, flowering longevity and ornamental value [12]. The cause of the increase in leaf greenness after PBZ application and the relationship between leaf greenness and photosynthetic capacity was investigated by ultrastructural observation
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