Table 5. Classical and non-classical secreted proteins based on the proteins identified in the cotton seedling xylem sap.

Secreted proteins	Qualitative peptides	Quantitative peptides in comparison	Non-quantitative peptides in comparison
			NLK	NNK	Others
Total	233	109	38	4	82
Classical	147	80	31	1	35
Non-classical	86	29	7	3	47

The identified proteins were predicted as classical secreted proteins using SignalP or non-classical secreted proteins using SecretomeP. More details can be found in Supplementary Tables 1 and 2.

Note: NLK: being non-detectable in low K; NNK: being non-detectable in normal K.