Seed Storage Protein Transcription and mRNA Levels in Brassica napus during Development and in Response to Exogenous Abscisic Acid

Abstract

Transcription rates and mRNA levels for Brassica napus seed storage protein families, cruciferin and napin, have been determined in embryos developing in the seed, as well as in embryos cultured with and without abscisic acid. Cruciferin and napin mRNAs are high during the cell expansion phase of embryo development, representing as much as 11 and 8%, respectively, of the total embryo mRNA. During the same time cruciferin and napin gene transcription rates, as measured in isolated nuclei, are also high. The data indicate that cruciferin mRNA is more stable than napin mRNA because while the napin transcription rate is higher than the cruciferin transcription rate, the cruciferin mRNA accumulates to higher levels. However, late in embryo development, both cruciferin and napin mRNAs seem to be less stable than earlier because comparable transcription rates result in lower mRNA levels. When embryos are cultured in the presence of abscisic acid, the levels of cruciferin and napin mRNAs are two-to threefold higher than in embryos cultured on basal medium. The transcription rates show a similar increase in the presence of abscisic acid, suggesting that abscisic acid is responsible for the increased mRNA level at least in part through an increase in the transcription rate of the two genes.Few proteins from plants have been studied as extensively as the seed storage proteins. By definition, seed storage proteins accumulate during the development of the seed, are stable during the period ofdevelopmental arrest that separates embryogeny from germination, and then are specifically degraded The pattern of expression of the storage proteins in B. napus has been followed by measuring protein accumulation (6) and mRNA levels (8,15) in embryos of different developmental stages. The major period of accumulation for both proteins begins during the cell expansion phase, which occurs about half way through seed development (25 dpa3) after tissues and organs have formed and cell division has ceased, and during which storage reserves increase. Napin accumulation stops about 20 d later (45 dpa), when the seeds are drying down (desiccation phase), while cruciferin accumulation continues until just before developmental arrest. Using cDNA clones, the mRNAs for napin and cruciferin can be detected quite early; napin mRNA is detected at 18 dpa just past the 'heart stage' of development and cruciferin mRNA can be detected 5 d later. Napin mRNA levels increase to their maximal level by 33 dpa while cruciferin mRNA levels do not peak until 38 dpa (8,15 Plant Physiol. Vol. 91,1989 seed storage protein mRNAs at rates comparable to development in the seed if 1 to 10 ,M ABA is included in the culture medium. In the absence of ABA, seed storage protein and seed storage protein mRNAs decrease to low levels.Regulation of storage protein expression during development and in culture is likely to be complex. For example, early embryos (27 dpa) cultured on ABA accumulate cruciferin mRNA and protein to levels comparable to that in the seed. Ho...

Distribution of Napin and Cruciferin in Developing Rape Seed Embryos

“…These results are in good agreement with earlier studies in which the amounts of napin and cruciferin were estimated by different immunological and biochemical techniques (3,14) and with experiments in which napin and cruciferin mRNA accumulation and transcriptional activity of the corresponding genes were determined during embryogenesis (5,16 of phytohemagglutinin, 3-conglycinin, and glycinin in different parts of the embryo (2,11,20). For both phytohemagglutinin and ,B-conglycinin, lower amounts ofthese proteins were detected in the axis.…”

Level of Abscisic Acid in Integuments, Nucellus, Endosperm, and Embryo of Peach Seeds (Prunus persica L. cv Springcrest) during Development

“…Moreover it could be involved in the regulation of storage protein synthesis, as indicated by other works (3,5,13).…”

Pattern of Variations in Abscisic Acid Content in Suspensors, Embryos, and Integuments of Developing Phaseolus coccineus Seeds

“…It has been shown that ABA is involved in the regulation of storage protein mRNA during mid-and late embryogenesis in embryos of rapeseed (8,9), soybean (4), and wheat (18,25). The major storage protein families found in P. coccineus seed are the vicilins, legumins, and phytohemagglutinins or lectins (3).…”