(68) The Role of Proteins in Leaf Re-greening

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  • 1 University of Nebraska, Agronomy and Horticulture, Lincoln, NE, 68583-0724

Common swedish ivy plants when exposed to nitrogen (N) stress display typical nitrogen deficiency symptoms such as reddening of stems and petioles and yellowing of leaves. When N levels are restored, leaves of swedish ivy plants will re-green without leaf loss. An experiment was conducted to determine how proteins change when leaves were re-greened after N deficiency. Cuttings of Plectranthus australis were rooted under mist and allowed to yellow. Plants were then potted up and fertilized with one of two treatments: complete nutrients with N at 150 ppm or complete nutrients with 0.8 ppm N. The experimental design was a randomized complete-block design with six blocks. Each block had the two N treatments and six plants per treatment. After 3–4 weeks, all plants in the 150-ppm N treatment had re-greened and leaf samples for protein analysis were taken. Plants in four of the six blocks were then switched to the other treatment. After leaves had re-greened once again, leaf samples were taken and the experiment was terminated. Two-dimensional polyacrylamide gel electrophoresis was used to compare the treatments. No obvious differences in protein absence or presence were noted. However, Rubisco appeared to be differentially expressed between the two treatments. 2-D gel analysis with subsequent Western blots showed that for most of the leaf samples, the large subunit of Rubisco (56kD) was quantitatively about 1.3 times more concentrated in the N-deficient plants and possibly modified. The small subunit (12kD) was not reliably detectable. Additional protein results for repeated leaf re-greening and the role Rubsico may play in leaf re-greening will be discussed.

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