Photosynthesis in Ranunculus asiaticus L.: The Influence of the Hybrid and the Preparation Procedure of Tuberous Roots

Abstract

Ranunculus asiaticus L. is a quantitative long-day geophyte, grown in a cold greenhouse for cut flowers and potted plants. Flowering in ranunculus is a complex process, strongly steered by temperature and photoperiodism. Vernalization of rehydrated tuberous roots anticipate sprouting and leaf rosette formation and flowering. It is known that the time for flowering and the sensitivity to cold treatment, in terms of flowering anticipation, varies in numerous hybrids, while no information seems to be available on the influence of hybrids and on the vernalization on the photosynthetic process and primary metabolite profiling. We investigated the influence of two ranunculus hybrids, MDR and MBO, and two preparation procedures of tuberous roots, only rehydration (Control, C) and rehydration followed by vernalization (V), on the photosynthesis and photochemistry of plants grown in a climatic chamber, under a controlled environment. In addition, in MBO plants, in which the vernalization showed the main effects, carbohydrate, amino acid and protein levels were also investigated. In control plants, the response of leaf photosynthesis, to increasing white light, revealed higher photosynthetic activity in MDR than in MBO. The quantum yield of PSII (ϕPSII), electron transport rate (ETR) and non-photochemical quenching (NPQ) did not differ between the two hybrids. The maximal photochemical efficiency (Fv/Fm) was higher in MBO than in MDR and showed a decrease in both hybrids after vernalization. The preparation treatment of propagation material affected the light response of photosynthesis in the two hybrids differently, which increased in plants from vernalized tuberous roots, compared to those from only rehydrated in MBO and decreased in MDR, in accordance to the effects of vernalization observed in leaf photosynthetic pigments. In MBO vernalized tuberous roots, starch was rapidly degraded, and the carbon skeletons used to synthesize amino acids. Control plants of MBO, developed more leaves than those of MDR and a consequent larger plant leaf area. Compared to only rehydration, vernalization of rehydrated tuberous roots increased the plant leaf area in both the hybrids. Compared to the control, vernalized tuberous roots of MBO showed higher concentrations of sucrose and free amino acids, which could act as a long-distance signal promoting floral transition in young leaf primordia.

The role of light quality of photoperiodic lighting on photosynthesis, flowering and metabolic profiling in Ranunculus asiaticus L.

“…Plant growth, in terms of number of leaves, plant leaf area, leaves and roots fresh and dry weights at the end of vegetative phase was higher in MBO than in MDR, confirming the occurrence of intrinsic difference in growth between the two genotypes, in agreement with our previous results on the same hybrids (Carillo et al 2019a).…”

“…In the present experiment, no significant difference in photochemistry was found between the two hybrids, conversely to our previous experiment in growth chamber under white fluorescence light, where PSII photochemical efficiency was higher in MBO compared to MDR (Carillo et al 2019a). This result could depend on genetic reasons and it was ascribed to the higher potential capability of MBO to convert light energy to reaction centers, particularly under sub optimal conditions in terms of both light intensity and spectrum.…”

“…Measurements of leaf NP in plants of R. asiaticus grown in greenhouse confirmed a higher photosynthetic capacity in MDR compared to MBO, we already observed plants grown in growth chamber under white fluorescence light (Carillo et al 2019a). No data seems to be available on photosynthesis in this species in literature, with the exception of our previous experiment in controlled environment performed in growth conditions very different compared to the actual experiment (200 μmol m −2 s −1 white fluorescence light at the canopy level, 20/18 C day/night Fig.…”

“…In particular, the photoperiodic treatment R:FR 3:1 increased minor amino acids including BCAAs, which may actively function as antioxidants and alternative electron donors for the mitochondrial electron transport chain (Woodrow et al 2017), limiting the occurrence of photo-oxidative damages. However, their increase appeared unrelated to the levels of hexoses, differently from Fritz et al (2006) and Carillo et al (2019a). On the contrary, in the EOD R:FR 1:3 light treatment, the Physiol.…”

“…In addition, since dormancy in bulbs is regulated by the balance of abscisic acid (ABA) and gibberellic acid (GA) (Liu et al 2011), vernalization releases dormancy by activating metabolic pathways involved in the down-regulation of ABA and primes biosynthesis of active GA forms (Wang et al 2018). However, a recent work from Carillo et al (2019a) showed that vernalization is not only able to induce a faster hydrolysis of starch reserves in R. asiaticus tuberous roots, but also it promotes a strong accumulation of hexoses and proline acting as compatible osmolytes and reactive oxygen species (ROS) scavengers. Moreover, the minor amino acids, whose accumulation is correlated to that of hexoses under stress (Fritz et al 2006), can act as antioxidant and/or an alternative electron donor for the mitochondrial electron transport chain accelerating plant metabolism and flowering (Woodrow et al 2017, Carillo 2018.…”