Cells in stalk could be classed into two categories according to the thickness of cell wall. Category one is the cell that only has a primary cell wall, such as parenchyma tissue cell, sieve cell, companion cell. Category two is the cell that has both primary cell wall and secondary cell walls, such as sclerenchyma cell (including fiber and hardened cell), vessel cell, tracheid cell, and collenchyma cell. Though there is cellulose both in primary cell wall and secondary cell wall. Lignin content in the secondary cell wall is high. Lignin is regarded as recalcitrance of stalk hydrolysis [21]. For bioconversion of stalk, the property for two kinds of cells would be different.

Besides, there are special cells with a different cell wall structure [19]. For a silicon cell, the cell wall is often silicified, and for dermal cell, the wall is usually hornificated. There are also secretory tissue cells including secretory cell, glandular hair, nectar, secretory sac. Secretory cell belongs to parenchyma cell, so their cell walls are rich in cellulose. Though there are few special cells in vascular plant, they affect bioconversion process. For example, hornification dermal cell is regarded as recalcitrance for enzyme hydrolysis [21].

Therefore, stalk is heterogeneous in the level of cell because of different com­ponents for a cell wall. So it is necessary to research their different conversion properties.

When corn stalk is pretreated with steam explosion integrated Bauer screening, two fractions could be obtained. The fraction bigger than 28 mesh contains more than 89 % fiber cell and the fraction smaller than 200 mesh contains 64 % parenchyma cell. Therefore, these two fractions are chosen to analyze the hydrolysis property of fiber cell and parenchyma cell. The fraction bigger than 28 mesh is crushed first to smaller than 200 mesh to remove the effect of a particle size. When two fractions are hydrolyzed for 48 h, glucose concentration is 5.15 g/L for parenchyma cell, which is two times higher than that of the fiber cell, and the hydrolysis rate of parenchyma cell reaches 70 %.

If corn stalk is fractionated with steam explosion integrated super grinding, pow­der fraction and residues fraction could be obtained. Parenchyma cell in powder fraction is 26.6 % higher than that of residues (area percentage), and fiber cell con­tent in residue fraction is 26.4 % higher than that of powder fraction [10]. Dermal cell content is also different in two fractions. Therefore, two fractions obtained from corn stalk pretreated by steam explosion integrated super grinding could be used to analyze the hydrolysis property of different cells. After hydrolysis for 24 h, reducing sugar content is 61.4 % for powder fraction, which is 3.8 times higher than that of residues [10].

The cell content before and after 48 h hydrolysis for powder fraction is analyzed. It reveals that fiber cell reduces by 22.8 % after hydrolysis. Parenchyma cell percentage reduces from 54.2 % to 7.3 %, while dermal cell percentage increases from 10.4 % to 80.9 %. These changes demonstrate that different cells have different hydrolysis properties. The enzyme hydrolysis property could be arranged as parenchyma cell > fiber cell > dermal cell [10].

In the process of pretreatment with steam explosion integrated super grinding, moisture content could affect fractionation results. If moisture content of steam ex­ploded materials is 40 %, the fiber cell content in residue fraction would be more than 60 %. Therefore, residue fraction could be applied to analyze fiber cell conversion properties.

Ethanol self-catalyzing method is applied for pulping. Pulping process is carried out at 180 °C for 2 h with 50 % ethanol concentration and solid-to-liquid ratio 0.8/10 (g/mL). It reveals that crud pulp yield of residue fraction could reach 61.4 %. How­ever, pulp yields of steam exploded rice straw and rice straw are 35.5 % and 32.1 %, respectively. So it demonstrates that there is positive correlation between fiber cell content and pulping property. Therefore, it would be an effective way to fractionate different cells and convert them, respectively.