Senescence-associated gene expression during ozone-induced leaf senescence in Arabidopsis - PubMed (original) (raw)

Senescence-associated gene expression during ozone-induced leaf senescence in Arabidopsis

J D Miller et al. Plant Physiol. 1999 Aug.

Abstract

The expression patterns of senescence-related genes were determined during ozone (O(3)) exposure in Arabidopsis. Rosettes were treated with 0.15 microL L(-1) O(3) for 6 h d(-1) for 14 d. O(3)-treated leaves began to yellow after 10 d of exposure, whereas yellowing was not apparent in control leaves until d 14. Transcript levels for eight of 12 senescence related genes characterized showed induction by O(3). SAG13 (senescence-associated gene), SAG21, ERD1 (early responsive to dehydration), and BCB (blue copper-binding protein) were induced within 2 to 4 d of O(3) treatment; SAG18, SAG20, and ACS6 (ACC synthase) were induced within 4 to 6 d; and CCH (copper chaperone) was induced within 6 to 8 d. In contrast, levels of photosynthetic gene transcripts, rbcS (small subunit of Rubisco) and cab (chlorophyll a/b-binding protein), declined after 6 d. Other markers of natural senescence, SAG12, SAG19, MT1 (metallothionein), and Atgsr2 (glutamine synthetase), did not show enhanced transcript accumulation. When SAG12 promoter-GUS (beta-glucuronidase) and SAG13 promoter-GUS transgenic plants were treated with O(3), GUS activity was induced in SAG13-GUS plants after 2 d but was not detected in SAG12-GUS plants. SAG13 promoter-driven GUS activity was located throughout O(3)-treated leaves, whereas control leaves generally showed activity along the margins. The acceleration of leaf senescence induced by O(3) is a regulated event involving many genes associated with natural senescence.

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Figures

Figure 1

Figure 1

SAG13 promoter-driven GUS activity was induced by O3 treatment. Fifteen-day-old Arabidopsis ecotype Landsberg erecta plants transformed with the SAG13 promoter-GUS fusion were exposed to 0.15 μL L−1 O3 for 6 h d−1 for 14 d. The fifth and sixth leaves were harvested from a single plant and GUS activity was measured by fluorometric quantification of 4-methyl umbelliferone (MU). Black bars, O3-Treated leaves; white bars, nontreated leaves. Each bar represents the mean of four samples ±

se

, except control bars on d 2 and 10, where the mean of three samples was taken. No GUS activity was detected in nontransformed plants (data not shown).

Figure 2

Figure 2

Photographs showing O3-induced GUS staining in the fifth leaf of transgenic SAG13-GUS plants. Fifteen-day-old SAG13-GUS plants were exposed to 0.15 μL L−1 O3 for 6 h d−1 for 14 d. Leaves were vacuum infiltrated with 1 m

m

5-bromo-4-chloro-3-indolyl β-

d

-glucuronide, incubated at 37°C for 72 h, and cleared of chlorophyll with 70% ethanol. Nontreated leaves are shown on the left and O3-treated leaves on the right from samples harvested 4, 8, 12, and 14 d after exposure in A through D, respectively. A similar pattern of expression was found in the sixth leaf (data not shown). The leaves shown are representative of three leaves per treatment per day.

Figure 3

Figure 3

Induction of senescence-related transcripts in O3-treated Arabidopsis plants. Fifteen-day-old plants were exposed to 0.15 μL L−1 O3 for 6 h d−1 or remained nontreated. Total RNA was extracted and 3 μg of RNA was separated on 1% formaldehyde-agarose gels, transferred to membranes, and hybridized with the radiolabeled probes indicated. A, Each lane contains RNA extracted from the fifth and sixth leaves pooled from six plants. The samples shown are one representative replicate from a total of three. B, Each lane contains RNA extracted from one rosette and only one replicate was analyzed. C, Control, nontreated plants; O3, O3-treated plants.

Figure 4

Figure 4

SAG12, SAG19, MT1, and Atgsr2 transcript levels were not altered by O3 treatment. Fifteen-day-old Arabidopsis plants were exposed to 0.15 μL L−1 O3 for 6 h d−1 or remained nontreated. Samples were prepared as in Figure 3. Each lane contains RNA extracted from the fifth and sixth leaves pooled from six plants. The samples shown are one representative replicate from a total of three. Sen, RNA sample extracted from yellowing (senescent) leaves older than 30 d; C, control, nontreated plants; O3, O3-treated plants.

Figure 5

Figure 5

PAG transcript levels declined after treatment with O3. Fifteen-day-old Arabidopsis plants were exposed to 0.15 μL L−1 O3 for 6 h d−1 or remained nontreated. Samples were prepared as in Figure 3. A, Each lane contains RNA extracted from the fifth and sixth leaves pooled from six plants. The samples shown are one representative replicate from a total of three. B, Each lane contains RNA extracted from one rosette and only one replicate was analyzed. C, Control, nontreated plants; O3, O3-treated plants.

Figure 6

Figure 6

SAG13, BCB, ERD1, SAG20, and SAG21 transcript levels declined following a recovery period in O3-free air. Fifteen-day-old Arabidopsis plants were exposed to 0.15 μL L−1 O3 for 6 h d−1 or remained nontreated. The fifth and sixth leaves were harvested from six plants immediately following 6 h of exposure to O3 or 18 h after removal of O3. Samples were prepared as in Figure 3. The samples shown are one of two replicates. C, Control, nontreated plants; O3, O3-treated plants.

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