Aluminum induced proteome changes in tomato cotyledons

Cotyledons of tomato seedlings that germinated in a 20 µM AlK(SO₄)₂ solution remained chlorotic while those germinated in an aluminum free medium were normal (green) in color. Previously, we have reported the effect of aluminum toxicity on root proteome in tomato seedlings (Zhou et al.¹). Two dimensional DIGE protein analysis demonstrated that Al stress affected three major processes in the chlorotic cotyledons: antioxidant and detoxification metabolism (induced), glyoxylate and glycolytic processes (enhanced), and the photosynthetic and carbon fixation machinery (suppressed).Key words: aluminum, cotyledons, proteome, tomatoDifferent biochemical processes occur depending on the developmental stages of cotyledons. During early seed germination, before the greening of the cotyledons, glyoxysomes enzymes are very active. Fatty acids are converted to glucose via the gluconeogenesis pathway.^2,3 In greening cotyledons, chloroplast proteins for photosynthesis and leaf peroxisomal enzymes in the glycolate pathway for photorespiration are metabolized.^2–4 Enzymes involved in regulatory mechanisms such as protein kinases, protein phosphatases, and mitochondrial enzymes are highly expressed.^3,5,6The chlorotic cotyledons are similar to other chlorotic counterparts in that both contains lower levels of chlorophyll, thus the photosynthetic activities are not as active. In order to understand the impact of Al on tomato cotyledon development, a comparative proteome analysis was performed using 2D-DIGE following the as previously described procedure.¹ Some proteins accumulated differentially in Al-treated (chlorotic) and untreated cotyledons (Fig. 1). Mass spectrometry of tryptic digestion fragments of the proteins followed by database search has identified some of the differentially expressed proteins (Open in a separate windowFigure 1Image of protein spots generated by Samspot analysis of Al treated and untreated tomato cotyledons proteomes separated on 2D-DIGE.

Table 1

Proteins identified from tomato cotyledons of seeds germinating in Al-solution

Spot No.	Fold (treated/ctr)	ANOVA (p value)	Annotation	SGN accession
1	2.34	0.001374	12S seed storages protein (CRA1)	SGN-U314355
2	2.13	0.003651	unidentified
3	2.0	0.006353	lipase class 3 family	SGN-U312972
4	1.96	0.002351	large subunit of RUBISCO	SGN-U346314
5	1.95	2.66E-05	arginine-tRNA ligase	SGN-U316216
6	1.95	0.003343	unidentified
7	1.78	0.009219	Monodehydroascorbate reductase (NADH)	SGN-U315877
8	1.78	0.000343	unidentified
9	1.75	4.67E-05	unidentified
12	1.70	0.002093	unidentified
13	1.68	0.004522	unidentified
15	1.66	0.019437	Glutamate dehydrogenase 1	SGN-U312368
16	1.66	0.027183	unidentified
17	1.62	2.01E-08	Major latex protein-related, pathogenesis-related	SGN-U312368
18	−1.61	0.009019	RUBisCo activase	SGN-U312543
19	1.61	0.003876	Cupin family protein	SGN-U312537
20	1.60	0.000376	unidentified
22	1.59	0.037216	unidentified
		0.003147	unidentified
29	−1.56	0.001267	RUBisCo activase	SGN-U312543
35	1.52	0.001955	unidentified
40	1.47	0.007025	unidentified
41	1.47	0.009446	unidentified
45	1.45	0.001134	unidentified
59	−1.40	5.91E-05	12 S seed storage protein	SGN-U314355
61	1.39	1.96E-05	MD-2-related lipid recognition domain containing protein	SGN-U312452
65	1.37	0.000608	triosephosphate isomerase, cytosolic	SGN-U312988
68	1.36	0.004225	unidentified
81	1.32	0.001128	unidentified
82	−1.31	0.001408	33 kDa precursor protein of oxygen-evolving complex	SGN-U312530
87	1.30	0.002306	unidentified
89	−1.3	0.000765	unidentified
92	1.29	0.000125	superoxide dismutase	SGN-U314405
98	1.28	0.000246	triosephosphate isomerase, cytosolic	SGN-U312988

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