Two Self-Incompatibility Sites Occur Simultaneously in the Same Acianthera Species (Orchidaceae, Pleurothallidinae)

Abstract

In most species of Pleurothallidinae, the self-incompatibility site occurs in the stylar canal inside the column, which is typical of gametophytic self-incompatibility (GSI). However, in some species of Acianthera, incompatible pollen tubes with anomalous morphology reach the ovary, as those are obstructed in the column. We investigated if a distinct self-incompatibility (SI) system is acting on the ovary of A. johannensis, which is a species with partial self-incompatibility, contrasting with a full SI species, A. fabiobarrosii. We analyzed the morphology and development of pollen tubes in the column, ovary, and fruit using light, epifluorescence, and transmission electron microscopy. Our results show that the main reaction site in A. johannensis is in the stylar canal inside the column, which was also recorded in A. fabiobarrosii. Morphological and cytological characteristics of the pollen tubes with obstructed growth in the column indicated a process of programmed cell death in these tubes, showing a possible GSI reaction. In addition, partially self-incompatible individuals of A. johannensis exhibit a second SI site in the ovary. We suggest that this self-incompatibility site in the ovary is only an extension of GSI that acts in the column, differing from the typical late-acting self-incompatibility system recorded in other plant groups.

Effects of Pollen Sources on Fruit Set and Fruit Characteristics of ‘Fengtangli’ Plum (Prunus salicina Lindl.) Based on Microscopic and Transcriptomic Analysis

“…In the present study, pollen tube growth in the self-pollinated flowers was severely hindered from the upper to the base of the style, which is consistent with Nikolic and Milatovic [ 48 ], who claimed that the incompatibility of plum ( Prunus domestica L.) occurs most often in the upper third of the style. Furthermore, abnormal morphology was often observed in incompatible pollen tubes, such as callose accumulation, apical branching, and tortuosity [ 40 , 49 ]. Irregular deposition of callose was noticed in the self-pollinated pollen tubes.…”

Challenges and Perspectives in the Study of Self-Incompatibility in Orchids

“…After self-pollination, the pollen tube growth of A. fabiobarrosii stops in the style ( Table 1 ). Aside from the style, the ovary was found to be the second reaction site of SI, and it might be an extension of the SI reaction in the style [ 33 ].…”

Self-Incompatibility of Camellia weiningensis Y.K. Li.

“…Self-pollinated pollen with the same genotype (including asexual reproductive materials) does not germinate on the stigma, or the germinated pollen tube cannot grow normally in the pistil, with the consequence that the fruit setting rate under self-pollination (the same genotype) is much lower than that under cross-pollination (different genotypes) [7][8][9]. In the cytological study of self-incompatibility reactions, fluorescence microscopy serves as the most efficient, most straightforward, and most convenient experimental means for observing pollen germination and pollen tube growth [10,11]. According to observations of pollen tube growth in the stigma and style of Camellia plants under a fluorescence microscope, when the pollen tube germinates in the stigma but cannot reach the base of the style, this is associated with the incompatibility of the pollen with the style canal [12].…”