Pollen of 18 of the 19 species of Eupatorium (sensu stricto) was examined with the scanning electron microscope (SEM). The species studied included the three dog fennels with dissected leaves and 14 species with undissected leaves. All species had echinate tricolporate pollen. One dog fennel, E. capillifolium, was found to have reduced spines relative to the other species. This one had other anemophilous characters, such as a longer stigma and greater stigma exposure, lax inflorescence branches, and smaller floral heads, suggesting an anemophilous pollinating system. Eupatorium compositifolium, another dog fennel, showed characteristics indicative of anemophilous ancestry, such as a long, greatly exposed stigmatic surface and lax inflorescence, but it had showy flowers as well as autecological features conducive to entomophily. All other species had reduced stigma lengths and exposure, stiffly upright inflorescence, and showy heads, all features indicative of entomophily. The advantage of acropetal over basipetal development of the inflorescence for anemophily is discussed. The dog fennels have acropetal, indeterminate development and the undissected leaf species have basipetal, determinate development; the latter of which is the basic pattern of inflorescence development in the Compositae.

Diploids of eight species of Eupatorium, triploids of three species, and tetraploids of four species are reported here for the first time. Meiosisin microsporocytes of triploids and tetraploids either failed to occur resulting in failure of pollen production or less frequently resulted in either incomplete chromosomal pairing or complete asynapsis; the latter two events lead to the production of grossly malformed, abortive pollen with unevenly deposited walls. Megasporogenesis examined in two polyploid plants led to the formation of eight-nucleate, unreduced embryo sacs which formed endosperm and embryos without pollination, indicating that the sporophytes develop asexually through agamospermy. Evidence is given that this may be a facultative characteristic. Megasporogenesis, studied in diploids of four species, produced normal embryo sacs with no indication of agamospermous development. Diploid plants of 11 of 12 species were tested and found to be self-incompatible.Since diploids could readily be distinguished from polyploids by pollen production (diploids produced normal pollen, polyploids produced none or malformed pollen), distributions of a large number of diploid, triploid, and tetraploid individuals could be determined from examining anthers of herbarium specimens. Distribution maps were made using these data as well as those from chromosome counts. Diploid members of species having both diploid, triploid, and (or) tetraploid members consistently had smaller distributional ranges than polyploids of the same species.

No abstract

The Really Interesting New Gene (RING)-type E3 ligase, Keep on Going (KEG) plays a critical role in Arabidopsis growth after germination and the connections between KEG and hormone signaling pathways are expanding. With regards to abscisic acid (ABA) signaling, KEG targets ABA-responsive transcription factors abscisic acid insensitive 5, ABF1 and ABF3 for ubiquitination and subsequent degradation through the 26S proteasome. Regulation of E3 ligases through self-ubiquitination is common to RING-type E3 ligases and ABA promotes KEG self-ubiquitination and degradation. ABA-mediated degradation of KEG is phosphorylation-dependent; however, upstream signaling proteins that may regulate KEG stability have not been characterized. In this report, we show that CBL-Interacting Protein Kinase (CIPK) 26 can phosphorylate KEG in vitro. Using both in vitro and in planta degradation assays we provide evidence which suggests that the kinase activity of CIPK26 promotes the degradation of KEG. Furthermore, we found that the kinase activity of CIPK26 also influences its own stability; a constitutively active version is more stable than a wild type or a kinase dead version. Our results suggest a reciprocal regulation model wherein an activated and stable CIPK26 phosphorylates KEG to promote degradation of the E3.