Induction of leaf senescence in Arabidopsis thaliana by long days through a light-dosage effect

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74662/1/j.1399-3054.1996.tb00463.x.pd

Isolation and partial characterization of dinoflagellate chromatin

Chromatin was prepared by two different methods from isolated nuclei of Gyrodinium cohnii (Cryptothecodinium cohnii) and Peridinium trochoideum. These isolation procedures are different from those generally used to prepare eukaryote chromatin, because the latter do not work for dinoflagellate chromatin. The chemical composition of this chromatin is similar for both methods of preparation and both organisms. Dinoflagellate chromatin contains DNA, RNA, acid-soluble and acid-insoluble protein as does chromatin from higher plants and animals, but the amount of acid-soluble protein relative to DNA (0.02-0.08) is much lower than that of typical eukaryotes (about 1). Evidence is presented to show that proteolytic degradation is unlikely to account for the low acid-soluble protein content in dinoflagellate chromatin. Exclusion chromatography of the chromatin on large-pore gels (Bio Gel A-15m or Sephadex G-200) indicates that the bulk of the protein present in the chromatin preparations migrates with the DNA. G. cohnii and P. trochoideum chromatin show an ultraviolet absorption spectrum, which is intermediate between DNA and typical eukaryote chromatin, and this is not significantly changed by gel exclusion chromatography. Preliminary results suggest that the dinoflagellate DNA-associated proteins do not stabilize the DNA against melting. Chromatin prepared from log-phase cells has more protein and RNA than chromatin from stationary-phase cells. The chemical composition of dinoflagellate chromatin is compared with that of prokaryotes and eukaryotes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22352/1/0000798.pd

Manipulating resource allocation in plants

The distribution of nutrients and assimilates in different organs and tissues is in a constant state of flux throughout the growth and development of a plant. At key stages during the life cycle profound changes occur, and perhaps one of the most critical of these is during seed filling. By restricting the competition for reserves in Arabidopsis plants, the ability to manipulate seed size, seed weight, or seed content has been explored. Removal of secondary inflorescences and lateral branches resulted in a stimulation of elongation of the primary inflorescence and an increase in the distance between siliques. The pruning treatment also led to the development of longer and larger siliques that contained fewer, bigger seeds. This seems to be a consequence of a reduction in the number of ovules that develop and an increase in the fatty acid content of the seeds that mature. The data show that shoot architecture could have a substantial impact on the partitioning of reserves between vegetative and reproductive tissues and could be an important trait for selection in rapid phenotyping screens to optimize crop performance

The role of the pod in seed development: strategies for manipulating yield

Pods play a key role in encapsulating the developing seeds and protecting them from pests and pathogens. In addition to this protective function, it has been shown that the photosynthetically active pod wall contributes assimilates and nutrients to fuel seed growth. Recent work has revealed that signals originating from the pod may also act to coordinate grain filling and regulate the reallocation of reserves from damaged seeds to those that have retained viability. In this review we consider the evidence that pods can regulate seed growth and maturation, particularly in members of the Brassicaceae family, and explore how the timing and duration of pod development might be manipulated to enhance either the quantity of crop yield or its nutritional properties

The Mode of Action of Maleic Hydrazide: Inhibition of Growth

Maleic hydrazide (MH) inhibits corn root elongation through an effect on cell division apparently without inhibiting cell enlargement. The decrease in the rate of elongation was apparent only after a considerable lag, over 14 hours, even with a concentration as high as 5 mM. MH (1 mM) did not inhibit His growth of roots from corn seeds given very large doses of Γ-irradiation or excised corn root segments including the elongation Zone or the cell enlargement induced by IAA in corn coleoptile sections. Many compounds including purines, pyrimidines, nucleosides. cysteine, pyridoxal, pyruvate. kinetin and CoCl 2 , many of which had previously been reported to alleviate MH inhibition in other tissues, were tested for their ability to prevent the inhibition of corn root elongation by MH, but none were effective. These data do not support the theory that MH acts by inhibiting the synthesis of or competing with some simple metabolite or hormone. Whatever its mechanism of action the failure of MH to inhibit cell enlargement in most systems indicates that it is fairly selective.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74891/1/j.1399-3054.1969.tb07375.x.pd

Proteomic changes associated with expression of a gene (ipt) controlling cytokinin synthesis for improving heat tolerance in a perennial grass species

Cytokinins (CKs) are known to regulate leaf senescence and affect heat tolerance, but mechanisms underlying CK regulation of heat tolerance are not well understood. A comprehensive proteomic study was conducted to identify proteins altered by the expression of the adenine isopentenyl transferase (ipt) gene controlling CK synthesis and associated with heat tolerance in transgenic plants for a C3 perennial grass species, Agrostis stolonifera. Transgenic plants with two different inducible promoters (SAG12 and HSP18) and a null transformant (NT) containing the vector without ipt were exposed to 20 °C (control) or 35 °C (heat stress) in growth chambers. Two-dimensional electrophoresis and mass spectrometry analysis were performed to identify protein changes in leaves and roots in response to ipt expression under heat stress. Transformation with ipt resulted in protein changes in leaves and roots involved in multiple functions, particularly in energy metabolism, protein destination and storage, and stress defence. The abundance levels of six leaf proteins (enolase, oxygen-evolving enhancer protein 2, putative oxygen-evolving complex, Rubisco small subunit, Hsp90, and glycolate oxidase) and nine root proteins (Fd-GOGAT, nucleotide-sugar dehydratase, NAD-dependent isocitrate dehydrogenase, ferredoxin-NADP reductase precursor, putative heterogeneous nuclear ribonucleoprotein A2, ascorbate peroxidase, dDTP-glucose 4–6-dehydratases-like protein, and two unknown proteins) were maintained or increased in at least one ipt transgenic line under heat stress. The diversity of proteins altered in transgenic plants in response to heat stress suggests a regulatory role for CKs in various metabolic pathways associated with heat tolerance in C3 perennial grass species

WRKY54 and WRKY70 co-operate as negative regulators of leaf senescence in Arabidopsis thaliana

The plant-specific WRKY transcription factor (TF) family with 74 members in Arabidopsis thaliana appears to be involved in the regulation of various physiological processes including plant defence and senescence. WRKY53 and WRKY70 were previously implicated as positive and negative regulators of senescence, respectively. Here the putative function of other WRKY group III proteins in Arabidopsis leaf senescence has been explored and the results suggest the involvement of two additional WRKY TFs, WRKY 54 and WRKY30, in this process. The structurally related WRKY54 and WRKY70 exhibit a similar expression pattern during leaf development and appear to have co-operative and partly redundant functions in senescence, as revealed by single and double mutant studies. These two negative senescence regulators and the positive regulator WRKY53 were shown by yeast two-hydrid analysis to interact independently with WRKY30. WRKY30 was expressed during developmental leaf senescence and consequently it is hypothesized that the corresponding protein could participate in a senescence regulatory network with the other WRKYs. Expression in wild-type and salicylic acid-deficient mutants suggests a common but not exclusive role for SA in induction of WRKY30, 53, 54, and 70 during senescence. WRKY30 and WRKY53 but not WRKY54 and WRKY70 are also responsive to additional signals such as reactive oxygen species. The results suggest that WRKY53, WRKY54, and WRKY70 may participate in a regulatory network that integrates internal and environmental cues to modulate the onset and the progression of leaf senescence, possibly through an interaction with WRKY30