Flower preformation in the nival plant Ranunculus glacialis L.: shoot architecture and impact of the growing season length on floral morphogenesis and developmental dynamics

Abstract

Flower preformation is a widespread phenomenon in perennial plants from temperate and cold regions. An advanced preformation status reduces the prefloration period and thus increases the chance to mature seeds in time. Despite the particular importance of this strategy for high-mountain plants, studies are rare. Here we investigated how the length of the growing season impacts floral development, and to what extent floral development is synchronized with reproductive phenophases in the arctic-alpine species Ranunculus glacialis L. The study was carried out in the alpine-nival ecotone in the European Central Alps at sites with different snowmelt dates. Individuals were sampled at regular intervals throughout the growing season, and shoot architecture and changes in floral structures were analysed in detail using different microscopic techniques. R. glacialis individuals consist of a cluster of independent ramets, comprising 3 sympodia each. Floral initiation terminates the vegetative growth of each sympodium 2–3 years before flowers become functional. A specific feature is that basal and distal leaves on a sympodium mature in different years. The date of snowmelt did not affect the speed of development but flower size and the number of lateral flowers within an inflorescence. Belowground floral preformation is closely linked to aboveground reproductive processes, however, continues below the snow in case winter conditions set in too early. The staggered preformation of architectural units creates a permanent belowground reserve pool of floral structures which might be advantageous in the climatically harsh and unpredictable high-mountain environment.

Transcriptomic Insight into Underground Floral Differentiation in Erythronium japonicum

“…Based on a previous report [ 45 ], we selected four stages of underground flower development in E. japonicum , and samples from each stage were subjected to transcriptomic profiling. A similar approach for exploring transcriptomic profile for floral differentiation has been adopted in different species such as Ranunculus glacialis [ 60 ], Chrysanthemum morifolium [ 61 ], Chrysanthemum lavandulifolium [ 62 ], Staphisagria Ranunculaceae [ 63 ], rice [ 64 ], and Delphinieae [ 63 ]. The obtained results in this study suggested significant variation in the expression profiles at the different stages.…”

Winter Frosts Reduce Flower Bud Survival in High-Mountain Plants

“…In the Central European Alps, the species occurs from the subnival to the nival zone at sparsely vegetated sites with sufficient snow cover in winter [ 84 ]. The overwintering belowground rhizome system consists of individually rooted bud-like ramets (see Figure 10 A) with alternate arranged leaves and a uni- to multiflorous inflorescence [ 55 , 87 , 88 ]. Winter-dormant terminal flower buds are in an advanced development state [ 55 ].…”

“…The overwintering belowground rhizome system consists of individually rooted bud-like ramets (see Figure 10 A) with alternate arranged leaves and a uni- to multiflorous inflorescence [ 55 , 87 , 88 ]. Winter-dormant terminal flower buds are in an advanced development state [ 55 ].…”

“…The majority of perennial high-mountain plants initiates flower buds in the year before anthesis by the conversion of vegetative shoot apical meristems into floral meristems, which develop further into single flowers or inflorescences [ 50 , 51 , 52 , 53 , 54 ]. Some species initiate flowers even two or more years before flowering [ 50 , 55 , 56 ]. Depending on the species, flower buds pass winter in different developmental states from early primordial to highly differentiated.…”

Why Is the Alpine Flora Comparatively Robust against Climatic Warming?

“…An important trait ensuring longevity and thus surviving both seasonal climatic extremes as well as disturbances is the below-ground position of apical meristems as well as cohorts of preformed flowering buds (e.g., [6,20]). Below ground stems and buds, rather slow clonal spreading and massive belowground storage organs [21] together ensure that alpine plants are hardly affected by the year-to-year variation of weather conditions.…”