Table 2. Expression levels and variation of 13 reference genes across four experimental sets in Saccharum officinarum.

Set		25S rRNA	18S rRNA	GAPDH	ACT	TUB	TIPS-41	CAC	CUL	UBQ	eEF-1a	eIF-4α	APRT	PRR
	Mean	14.55	15.56	25.04	25.7	26.97	29.1	27.71	26.59	26.24	24.14	27.91	27.32	27.96
1st set	SD	0.83	0.4	0.79	0.91	1.04	1.09	1.33	1.37	1.3	0.96	0.98	1.14	1.43
	CV	5.72%	2.57%	3.16%	3.53%	3.86%	3.76%	4.78%	5.15%	4.94%	3.96%	3.52%	4.19%	5.10%
	Mean	13.88	15.28	23.95	24.46	27.22	27.5	27.53	26.88	26.29	23.81	27.72	26.59	27.15
2nd set	SD	0.27	0.95	0.74	0.79	2.47	2.41	0.92	0.94	0.74	0.88	0.75	0.99	1.07
	CV	1.96%	6.24%	3.08%	3.22%	9.07%	8.77%	3.35%	3.50%	2.82%	3.70%	2.69%	3.71%	3.94%
	Mean	14.28	15.39	24.71	24.9	26.89	27.9	28.26	27.59	26.81	24.66	28.35	27.82	29.05
3rd set	SD	0.74	0.83	1.63	0.97	0.91	2.22	1.67	1.72	1.52	1.85	1.75	1.67	2.88
	CV	5.15%	5.40%	6.59%	3.88%	3.39%	7.96%	5.91%	6.24%	5.68%	7.49%	6.16%	6.00%	9.90%
	Mean	14.08	15.25	24.38	24.58	26.87	27.42	27.99	27.35	26.62	24.31	28.02	27.37	28.37
4th set	SD	0.57	0.87	1.39	0.92	1.64	2.4	1.46	1.51	1.28	1.52	1.38	1.5	2.35
	CV	4.04%	5.72%	5.72%	3.73%	6.10%	8.75%	5.23%	5.51%	4.82%	6.27%	4.94%	5.50%	8.29%

Mean Ct value (Mean), Standard deviation (SD) and Covariance (CV) were calculated by Microsoft Excel 2003. 1^st set: leaf, leaf sheath, stem epidermis,stem pith and bud from “ROC”20, “ROC”22, FN40, liucheng03-182 and YC05-179; 2^nd set: ABA, MeJA and SA, treated-samples from “ROC”20, FN40, Liucheng03-182 and YC05-179; 3^rd set: H₂O₂, NaCl, PEG, CuCl₂ and CdCl₂ treated-samples from “ROC”20, FN40, liucheng03-182 and YC05-179; 4^th set: 2ⁿset+3^rd set.