How Does <Emphasis Type="Italic">Mimulus verbenaceus</Emphasis> (Phrymaceae) Set Seed in the Absence of Pollinators?

Mimulus verbenaceus has successfully invaded and/or competed for the very specialized habitats of desert seeps and springs characterized by scarce or no pollinators (personal observation). It has done so by evolving an ingenious mechanism of reproductive assurance in which the senescing epipetalous corolla bends down, abscisses and slides down its style dragging its anthers over the stigma lobes, resulting in self-pollination. This dragging mechanism both depends on the plants ability to self-pollinate and presumably promotes the evolution of self-pollination by providing an advantage—invasion of new habitats—to counter-balance the disadvantages of selfing. M. verbenaceus has evolved a second means of reproductive assurance that depends on the nearness of the anthers to the stigma lobes. They are close, even touching, in the red flowers, leading to much self-pollination and are well separated in the yellow flowers leading to little self-pollination. This advantage of the red-flowered plants likely explains the relative abundance of the red morph and the rarity of the yellow morph in nature as well as the greater seed set of the red-flowered morph than that of the yellow-flowered morph.     

花器官决定的ABC模型和四因子模型

简要介绍了花器官决定的同源异型基因作用模型--ABC模型的产生和发展过程.从早期ABC模型发展到经典ABC模型,然后到ABCD模型,最后到A-E模型.花器官发育遗传学的创立和发展是ABC模型产生的基础,ABC模型的建立促进了花器官发育遗传学的发展,而后者进一步发展的结果又促使前者更加完善,从而进一步发展为四因子模型.     

MADS-box基因对花的发育及开花早晚的影响

介绍了植物中MADS-box基因和MADS-box蛋白转录因子的组成,MADS-box基因是一类序列特异的多基因家族,所编码的蛋白即为MADS-box转录因子,它是以二聚体化的形式通过其保守结构域与特定的DNA序列相结合来调控基因的表达.主要介绍了ABC模型及MADS-box基因与花的发育,并介绍了可促进开花的4种MADS-box基因-AGL20、AGL24、CO和SOC1及抑制开花的另外4种MADS-box基因-FLC、FLM、FRI和SVP,最后提出前景和展望.     

花衰老过程中的生理生化变化及对花衰老的调节(综述)

本文概述花衰老过程中的多种生理生化变化以及各种影响因素的调节作用。     

Patterns of color and nectar variation across an Ipomopsis (Polemoniaceae) hybrid zone

Hybridization may uncouple adaptive trait combinations that are present in parental species. I studied variation in flower color and reward quality across a hybrid zone of Ipomopsis aggregata and I. tenuituba. Individuals from hybrid populations showed considerable variation in flower color using corolla reflectance measurements. Flower spectra of such individuals were either intermediate or else resembled those flowers from the parental species. Ipomopsis aggregata populations had consistently higher nectar production rates and higher nectar standing crops than either I. tenuituba or hybrids. Ipomopsis aggregata flowers also produced more dilute nectar than those of hybrids and I. tenuituba, but the actual concentration values were quite variable among populations of the same type. Overall, the nectar quality of hybrid flowers most resembled that of I. tenuituba flowers. Based on the observed interpopulation patterns of color-reward associations in this hybrid zone, pollinators should be able to discriminate against I. tenuituba and hybrid populations and against most individuals within hybrid populations. However, they may visit those hybrids that resemble the most rewarding flower type (I. aggregata). The results emphasize the need for studies that address how hybridization affects subsequent plant fitness and the evolutionary dynamics of the species involved.     

Is the Root Effect on Flowering of Chenopodium rubrum Mediated by Cytokinins?

Root removal enhances flowering in the short day plant Chenopodium rubrum. The extent of this effect depends on the de-rooting time with respect to photoperiodic induction. The largest promotive effect is observed when de-rooting coincides with the start of the inductive treatment or, to a lesser extent, when performed before it. De-rooting 24 h after induction has no effect on flowering. The flower-inducing action of de-rooting 24 h before the start of induction is increased by benzylaminopurine (BAP), whether applied simultaneously with de-rooting or 24 h later. At the beginning of darkness, BAP inhibits flowering slightly when applied simultaneously with de-rooting but inhibits it strongly when applied 24 h later. Flowering in plants de-rooted 24 h after induction is inhibited strongly by BAP. Root removal at the beginning of inductive darkness does not change the level of endogenous cytokinins in induced shoot explants, but under continuous light the level of cytokinins in shoot explants decreases during the same period compared with the level in the shoots of intact plants. BAP does not affect the level of endogenous cytokinins in light but causes an apparent increase in induced segments. Thus, two phases of the de-rooting effect and cytokinin treatment may be distinguished: one in which flowering is enhanced by both treatments and which is linked directly to photoperiodic flower induction, and the other in which both treatments are inhibitory to flowering and which is related to morphogenetic events following induction. The time courses of the effectiveness of de-rooting and BAP treatment differ slightly, suggesting that the effect of de-rooting cannot be attributed solely to cytokinin deprivation. Received February 27, 1998; accepted March 3, 1998     

Horizontal orientation of zygomorphic flowers: significance for rain protection and pollen transfer

• Floral traits are recognized to have evolved under selection for abiotic and biotic factors. Complex zygomorphic flowers usually face horizontally. It has been proved that a horizontal orientation facilitates pollinator recognition and pollination efficiency, but its significance in adaptation to abiotic factors remains unknown.
• The floral orientation of Abelia × grandiflora naturally varies around horizontal (with an angle of ?30 to +33° between the floral main axis and the horizontal). We examined whether three different floral orientations affected flower thermal conditions, response to rain and pollination.
• Results showed that floral orientation had no effect on diurnal variations in flower temperature. The anthers of all three flower orientations were wetted by rainfall, but the inclined upward‐facing flowers contained significantly more rainwater. The horizontal flowers received significantly higher visitation by hawkmoths and had a higher stigmatic pollen load. In contrast, the upward flower orientation reduced pollination precision, while downward‐facing flowers had decreased pollinator attraction.
• This study indicates that horizontal flowers may have evolved as a trade‐off between rain protection and pollination. Zygomorphic flowers that deviate from a horizontal orientation may have lower fitness because of flower flooding by rainwater and decreased pollen transfer.

     

The Shoot Apex as a Marker of the Responsivity to Photoperiodic Treatment Inducing Flowering of Chenopodium rubrum L.

Two maxima in flowering response to one inductive dark period of 13 h were found in the short day plant Chenopodium rubrum within three weeks of cultivation under continuous illumination either in vitro or in vivo. These maxima correlated with the number of leaf primordia and their relation to the size of the apical meristem. The first maximum in flowering responsivity corresponded with the stage when primordia of the second leaf pair had not yet overtopped the apical meristem, the second one when the primordia of the fourth leaf overgrew the meristem. Maximum responsivity to flowering reached by a mother plant was reflected in explants derived from it. The above morphological markers of responsiveness to floral induction were not linked to plant age and/or to general growth habit. The explants flowered only when part of the stem was present.