The Origin and Identity of the Calyculus in Loranthaceae:Inferred From the Floral Organogenesis of Loranthus tanakae Franch.&Sav.

The flowers of the hemiparasitic family Loranthaceae are always subtended by a rimmed structure known as the calyculus.The origin and identity of the calyculus have been disputed for more than a century.Various hypotheses have been proposed,for example,an outgrowth of the axis,a reduced calyx,and a bracteolar(prophyllar)origin,but controversies remain.To obtain a plausible explanation of the origin of the calyculus,we investigated the flowers of Loranthus tanakae using scanning electron microscopy and light microscopy to observe the entire developmental process of the floral parts.Our results show that bracts are not present in L.tanakae.The calyculus,which lacks serving vascular bundles,initiates as a semicircular primordium and then develops into a circular structure by an adnation at both sides.The flower primordium usually cleaves into six petals from its centre along a whorled pattern in two series with three petals each,before or after the calyculus closed.Isomerous stamen primordia probably follow the same initiation pattern as petals do.Several carpels of different sizes initiate simultaneously as a united primordium.We support the hypotheses that the calyculus is of bract or bracteole origin due to its independent initiation from the inflorescence rachis,its similar morphology and positioning as the bract or bracteole,and that having no developmental relationship with the petals.We suggest keeping the usage of the term“calyculus”.Loranthus flowers should be considered monochlamydeous with three whorls of floral parts,namely petal,androecium,and gynoecium.

Bract suppression regulated by the miR156/529-SPLs-NL1-PLA1 module is required for the transition from vegetative to reproductive branching in rice

Reproductive transition of grasses is characterized by switching the pattern of lateral branches,featuring the suppression of outgrowth of the subtending leaves(bracts)and rapid formation of higher-order branches in the inflorescence(panicle).However,the molecular mechanisms underlying such changes remain largely unknown.Here,we show that bract suppression is required for the reproductive branching in rice.We identified a pathway involving the intrinsic time ruler microRNAI56/529,their targets SQUAMOSA PROMOTER BINDING PROTEIN LIKE(SPL)genes,NECK LEAF1(NL1),and PLASTOCHRON1(PLA1),which regulates the bract outgrowth and thus affects the pattern switch between vegetative and reproductive branching.Suppression of the bract results in global reprogramming of transcriptome and chromatin accessibility following the reproductive transition,while these processes are largely dysregu-lated in the mutants of these genes.These discoveries contribute to our understanding of the dynamic plant architecture and provide novel insights for improving crop yields.

Pollinator attraction in Cornus capitata (Cornaceae): the relative role of visual and olfactory cues

Aims it is generally accepted that visual displays and floral scent play important roles in communication between flowering plants and their pollinators.However,the relative role of visual and olfactory cues in pollinator attraction is largely unknown.in this study,we determined the roles of both types of cue in attracting pollinators to Cornus capitata,a medium sized tree with each capitulum sur-rounded by four large,white,petaloid bracts.Methods Pollinator observations and pollination experiments were con-ducted in a natural population;the inflorescences’visual and olfactory signals were characterized by spectral and chemical analyses;the responses of pollinators to visual and olfactory cues were tested using dual-choice behavioural bioassays;the relative roles of visual and olfactory cues in pollinator attrac-tion were tested by comparing the responses of pollinators to inflorescences subjected to three experimental treatments(intact,all bracts removed,and capitulum removed)within the natural population.Important Findings For fruit set,C.capitata is entirely dependent on pollinators,with a bee,Anthophora sp.,being the main pollinator.bracts present high colour distance and green contrast against the leaves.Twelve volatile compounds in the floral scent were detected,most of which have previously been reported to be attractive to a broad spectrum of bee species.behavioural bioassays showed that both,visual cues alone and olfactory cues alone,are attractive to pollinating bees.However,vis-ual cues alone attracted significantly more approaches than olfactory cues alone,while olfactory cues alone elicited a significantly higher landing percentage than visual cues alone.The finding suggests that,in the C.capitata-Anthophora sp.interaction,visual cues are mainly used for location from long distances,while olfactory cues mainly aid landing from short distances.our results indicate that different modalities of floral cues should be considered together to understand fully the communication between flowering plant and pollinators.